How'd you decide on a '91 instead of a '92? I agree the '93 got cheezed out just a little in a few areas (no matter what you do or don't think of the Northstar), but couldn't you go with a '92 and have same engine as a '91 but with a few other minor upgrades?
Anyways, We've only had our '88 Allante with 115k miles for about 2500 miles now (less than a month for us) and though the car runs perfect, and seems to have been well taken care of (mostly garaged) with both tops (I swear I don't think she hardly ever put the soft top up) we have had some electrical issues, the problem though is that they don't REALLY seem to be issues, we're just getting error messages from the DIC about low fluid levels on things yet when I check the levels they're just fine. Some of the switches on the seat controls don't seem to work right but I think that's natrual for a convertable of this age, there is a little corrosion in the switches no doubt.
We've had 5 Jeep Grand Cherokee Limites in a row, all with full-time 4x4 and all with V8 engines, a '95, '98, '99, 01, and '03 and have ran all of them to OVER 300+ thousand miles before selling them. Much of the time pulling a 22 foot Twin-V8 ski boat all over the ozarks during the summers. But this summer we bought a bigger boat and got a perminant slip at the lake, so didn't need the towing capacity of the Jeeps so decided to get a "touring" car. We set out with a Mid-to-Late '90s Eldorado ETC in mind but ended up with the Allante, a car I've always liked. By comparison to the Allante with it's 115k miles and the problems I listed we never had ANY problems of any kind with any of the Jeeps, even up past 300k miles, one of which I sold to a college student son of some friends who's now drove it for two years and now has over 400k and still going strong.
The more I have talked with other Cadillac owners and Allante owners (and other GM owners, used to hear tales of their bad experiances with their big GM model SUV's at the boat docks cussing all of their problems with relativley few miles, and we'd just smile as drive off in our ultra-high miledge Jeeps that we'd never had a problem with of any kind (and got 25mpg when not pulling the boat). So some of it comes down to experiance. If you ask another GM product owner they'll probably think the issues they've had are "normal" for everyone, just as I would if you asked about my '87 Jaguar XJS-C V12 compared to other Jaguars, but if you compare them with someone who's owned something like a Grand Cherokee who's never known any problems then by comparison it sounds like they have allot of problems. I am kind of begining to worry that the sheer miles that we put on our cars may be a bit much to expect of the Allante from what I'm reading. I'm kind of considering going back to my original idea of an Eldorado ETC... Who knows, maybe I'll find someone who wants to trade.
I myself am an enthusiast, I own several cars that could be considerd collectable, exotic, or unique including everything from my '67 GTX Convertable, '71 Cuda 340+6 4 Speed, '65 Olds 442, to newer models like an '87 Jag XJS-C V12 and a '93 Mitsubishi VR-4. All nice cars but we're at the point we want to do allot (as though we didn't already) of traveling this summer and wanted a larger car with decent fuel miledge and a real trunk, believe me, a '67 Belvidere GTX has a large trunk but no MPG's, the VR4 had great fuel miledge but no truck space. The Jaguar V12 actually gets 23 MPG crusing at 85 (and you thought V12s got bad MPG's) but would be darn finiky if I had to find a shop for her out on the road.
So my short (or rather long) answer is that it depends on what YOU are going to do with it. Even if I decide to get an Eldorado we may still keep the Allante for my fiancee to drive back and fourth to school (shes a teacher) during the spring and fall and run around town in the summer in. She really likes it and I've already told her she could have it if she wanted it though she's a little old fashioned and said she'd take it if we were married but since we're not getting married until April she'd keep her current car (Hond Accord LXi) for now. Actually after loosing my first fiancee nearly 9 years ago to a drunk driver I once told her that I was going to buy her the largest SUV that Volvo makes and have it renforced by Hess & Esenheart (My last "company" vehicle was armoured by them).