Don't know why this came to me within the last day or two but I'm going to bounce it off all of you to see what the reaction is.
I thought of the Audi 5000 Quattro Turbo the other day and I suddenly realized that you never see them any more. At the time they were introduced the car magazines proclaimed them just about the perfect car and I can't remember the last time I saw one, let alone heard anyone refer to one.
So what's the deal, did they all rust away, or did the replacement cost of the turbo/drivetrains ultimately total them? Is it something I should be looking for or are they money pits?
A VW-Audi repair shop about 45 minutes from where I live has at least 1 or 2 Audi 5000s in it's "awaiting service" area....and they have been there almost forever.
I think many folks who bought these cars new moved on to more expensive German brands (BMW or M-B) or went over to the not quite as expensive to buy/maintain Japanese luxury brands. The few times I've been to my local pull-apart, I've never seen an Audi (or a BMW or M-B, so it may be I was in the wrong area), but did see dozens of nearly rust-free and usually UN wrecked Volvos.
Here's the problem with the 5000 Turbo.
There's a lot of 4000s out there, and the 5000 Turbo's engine is a near bolt-in. Just have to do a little exhaust jiggery, bend the passenger side tie-rod, and relocate the battery. You could even do it all with OEM parts if you felt like spending money. (everything in the way on a 4000 can be sourced from an ur-quattro)
Did I mention that you can apparently get running/driving 5000 Turbos with electrical problems or failed automatics (or both) for absurdly low prices?
Note that until about 1991-ish, if it was AWD, it wasn't an automatic.
Anyway, a lot of people who do engine swaps in a 4000 start out by buying an entire 5000, driving it home, pulling the engine, and scrapping the shell. It reminds me of the shark fishermen who catch the shark, cut the fins off, then throw the shark back into the water... anyway, the engine is the most bulletproof part of the car. IIRC they don't rust, either. Galvanizing.
(says the guy who has a B2 chassis sitting in the driveway, and two ex-5000 Turbo engines in the garage)
What he said.
They were tanks. Great higher end cars for long distance but not really so nimble you'd ever want to autocross one. Like any high end luxury car, they depreciated like a rock (plus they suffered from the Unintended Acceleration debacle). This in turn sent them into the hands of people who wouldn't or couldn't afford to maintain them, so they quickly became expensive nightmares. They were never as simple or inexpensive to fix as the (better) 4000's. Climate control modules failed. Blower fan motors failed (and they were an absolute nightmare to replace). Power accessories failed. Power steering systems would leak. Auto trans problems. Uber-expensive parts. They very quickly became donors for 4000 quattro turbo swaps. They were not necessarily bad cars, but they were far, far more expensive to fix than the 4000 was.
it was rare, even the 90's , to find a 5000 without several "rewires." rad fan fixes, under dash items, etc. Ill second (3rd, 4th?) the above, the 4kq was a much more reliable model, and handled wonderfully in comparison.
OTOH the 5kq was a GREAT distance runner. when I lived in the northeast, I used to ski alot. if we were on a day trip, wed take my 4kq, but if were going up to killington or any of the other big mountains, my friends 5kq was always the better choice, at least when it was functioning properly. 
A friend of mine who likes to tinker on German cars acquired a 5000 a few years back. I was impressed with the size of the car--it was as big as a gym inside! You could play volleyball in there.
Ultimately the car proved to be a major headache with a fuel tank full of rust and resultant fuel injection problems.
Figuring out the unintended acceleration problem was a no-brainer, since the brake pedal pad on this automatic car was the same size as you'd find in a stickshift car, and placed quite close to the gas pedal.
