Should I buy a boat with IPS drives?

I've just seen the very simple question in the thread title, and I thought it deserved a very simple answer.
In which case, my own would be no.
Then again, I'm not sure it makes sense to expand further.
It seems that the OP disappeared, after throwing the rock into a pond...

Well, I'm always a bit wary of dismissing something, because strong criticisms often spark divisive debates.
And of course, personal experiences are... ermm... personal, so the YMMV principle is always valid.

But since you asked, below is my 2c, in no particular order.
With a premise: I'm only comparing IPS with shafts, not with outdrives - whose place is imho restricted to smallish speedboats.

1) one inherent defect of fwd facing pods is that they are prone to grab even the smallest bit of line, which quite often damages the shaft seals, contaminating the oil with salt water.
This means a liftup and props removal+seals replacement at best, and a whole pod replacement at worse. Either ways, $$$.
In comparison, I can recall of at least 3 lines which I grabbed with my shaft powered boats.
All of them ruined my day, but it only took a sharp knife and a tank of air to get rid of the problem.

2) another inherent defect of pods (this time, regardless of their orientation) is that on planing hull they emphasize the listing upon steering at speed, because their vector thrust does not rotate along a vertical axis, but a diagonal one - as diagonal as the hull deadrise.
As a consequence, builders are faced with the choice between two evils: either flatten the hull section astern, where pods must be installed (which in turn makes the boat more prone to slamming in head seas), or accept a rather scary behaviour while steering at speed (which is something that usually don't impress prospect clients upon sea trial - and rightly so).

3) in terms of maintenance, on top of being already very expensive to do what VP recommends, sometimes it's not even enough. I'm aware of some cases where, in spite of having always strictly followed the echelon, the dreaded emulsionated oil or the notorious friction defect popped out of the blue, ruining the whole holiday of the boater involved.

4) for any comparable installation (similar boat size/weight), the IPS fuel savings are nowhere near the 30% claimed by VP - not even remotely.

5) the joystick is particularly attractive for inexperienced helmsmen, and there's nothing wrong with the principle of simplifying life to newcomers, of course. But as it happens, the very same joystick can become dangerous, in not sensible enough hands.
I personally witnessed the case of a boat mooring stern to in between two other boats (and I appreciate that this is rare in the US, but it's the norm in the Med), where after reversing the boat reasonably well in its space, the helmsman used the throttle a bit too much to keep the boat from moving sideways.
This made the boat, before even beginning to move sideways, to list so badly on one side that the walkaround rail of the boat collided with the other one on her side, in spite of the fact that both boats were well fendered along the hull.
Thanks God, nobody on those boats were grabbing the rail with their hands in the fraction of second when that happened. Since one of the rails involved was bent (!), it's easy to guess what could have happened to any hands/fingers in between.
And aside from this possibly extreme case, seeing IPS powered boats which suddenly list either side at the touch of the joystick, overbalancing the crew caught by surprise, is becoming typical enough to spot them (and their helmsmen ability ) from some distance, when they approach a marina...

See? I did say that YMMV, didn't I?
Btw, when you are talking of the IPS powered boats that you ran, they were not YOUR boats, I guess?
I'm just assuming that yours is the timeless one in your avatar, which implies that you didn't choose IPS for yourself, no matter how well the ones you ran performed.

It's a bit like Azimuts, really: they aren't loved by professionals, who wouldn't want one for themselves - and neither would I.
BUT, they keep selling like hot cakes, and in their segment they are among the most popular boats in the planet, whether YF members like it or not.
By the same token, I'm aware that IPS boats (some - certainly not all) can be nice to run.
But I'm happy to leave them all available for anyone else interested in them.

Just one comment about your reply, ref.5:
I don't think I'm wrong, and not because I'm always right (don't we all think to be?! ), but because it ain't a matter of right or wrong.
The problem is that the pods are powerful enough to push the boat sideways VERY rapidly (mind, I was NOT talking of twisting the knob to spin the boat on her own axis, but of lateral-only movements, by pushing the knob either to port or stbd).
On top of that, the pods force vector (in contrast with traditional thrusters) is always diagonal rather than horizontal, whenever the computer rotates the pods in order to move the boat sideways.
This means that there are two force components applied on the hull, whereas the vertical one is totally undesired but inevitable, and only translates in listing/rolling - in direct relationship with the total force applied.
So, VP usually suggest boatbuilders to program the control unit for limiting the max power applicable upon maneuvering, no matter how hard the helmsman pushes the knob.
If you tried some of these boats, you are unlikely to have noticed anything strange, but probably they couldn't move sideways as rapidly as theoretically possible.
On the other hand, since the same result of smoothing sideways movements can also be achieved simply by being gentle with the knob, some other builders prefer to leave the choice to the helmsman, allowing more power to be applied upon translations, if and when the knob is pushed hard.
Also because many newbies like that, since it reminds them of the behavior they are used to with their car, whose reactions are much more immediate than with any boat.
Trouble is, upon the first moment of panic that sooner or later is bound to materialize, they tend to use the knob like there's no tomorrow - with the results I previously described.
And which you might find hard to believe I suppose, but aside from telling you that I was there, and that the captain of the damaged boat asked me if I could give him my whereabouts as a witness for the insurance claim, I don't know what else I can say.

Haha, nope, actually the Capt I previously mentioned was already docked, and it's his boat that ended with a bent rail.
The offending IPS-powered boat was maneuvered by her owner, and pretty sure he wasn't one of your students.
Or a student of any experienced teacher, for that matter!

Ref vectorial forces, sorry if I got carried away by technicalities, anyway the effect I mentioned does NOT depend on whether the pods are controlled by the wheel or by the joystick.
It depends on the fact that pods are installed on the bottom of V-shaped hulls, as opposed to commercial pods installed on tugs, ships, etc.
That's in fact where pods began to be adopted, MANY years before VP had the brilliant idea of arm-twisting the concept also into planing hulls.
Just think of outdrives, or rudders of shaft powered boats, or also commercial pods: all of them rotate along a vertical axis, as it should be.
But with IPS, the rotation axis is instead diagonal - as much as the hull deadrise (deeper vee = more diagonal rotation), and there's no way round it.
This is the anomaly that all IPS installations must deal with, and that requires several compromises.
The joystick can emphasize the effect when handled too nervously upon close quarters maneuvering, of course. But also when hard steering at speed with the wheel, the higher listing (compared to any other propulsion) induced by diagonal thrust remains exactly the same.
The extent of that depends on many factors, and there are boats where it's barely noticeable, but also others where it's downright scary.

Sorry also for the YMMV acronym, it isn't nautical actually, more internet-driven in general.
Just click here for a brief explanation.

Far from being a SF expert, but your numbers strike me as evidence of a bad shaft hull, first and foremost.
What happened at Cabo, did they forget how to build a decent boat on shafts?
A quick search for Cabo 40 pointed me to a 2003 test published by SF Mag.
According to it, back then the boat was capable of 42 mph top, and 35 mph (~30kts) @ 1800, burning 43 gph.
A number that makes MUCH more sense than the 63 gph, and that corresponds to 1.4 G/Nm, instead of 2 G/Nm.
That's a 30% savings with the older model (which btw was powered by the non-CR 700hp MANs, go figure!) vs. the boat you mentioned, both on shafts. Whiskey Tango Foxtrot?

Now, even without knowing anything about the more modern version of the 40' that you mentioned, I can already tell that she doesn't have the same hull, because the 2003 model had a decent aft deadrise of 16.5 degrees, which is not IPS-compatible due to the inherent defect I previously mentioned, and that Liam specified further.
So, my guess is that they redesigned the hull specifically for IPS installation, and then adapted shafts on it, rather than the other way round.
Which make the numbers you quoted not exactly surprising, since they are due to a bad shafts hull - Q.E.D.

All that aside, there is one general consideration that you should always bear in mind: any boatbuilder who decided to go down the IPS road will always praise the results achieved.
Pretty sure you never saw an advertisement along the lines of...
"We adopted IPS strictly because VP give us great discounts, to enlarge the number of installed packages, in order to make money with maintenance afterward. And on top of that, IPS also allows us to install the powerplant faster and with less skilled manpower.
There are several drawbacks we are well aware of, obviously. The most noticeable one being the fact that we will have to trade seaworthiness for the IPS installation requirements.
But let's not forget the IPS advantages for you, like the joystick for those who don't have a clue about how a boat should be handled, and the larger interiors because we can squeeze the e/room to the point that mechanics will go nuts, eventually costing you even more.
But hey, boats are just toys for rich boys anyway, aren't they?"
Now, do you know why you never saw anything like that?
Because it would be true, that's why.

Hang on, I just noticed that your comparison was between a shaft and a Zeus (not an IPS) boat, and that does make a difference.
My previous post was obviously focused on IPS, which is what we discussed so far.
The comparison between the 2003 Cabo 40' and the one you mentioned remains equally hard to justify, anyhow.
63 gph is more of what my 800hp MANs burn on a 56 footer that weighs more than twice the Cabo 40...?!?