I'm very new to e34's, but just bought a 520i vanos last week. Here is my story. It was the 4th e34 i met since I started my hunt. The car from first sight seemed very clean and the engine bay as well. Comparing to the first three it seemed the cleanest. Took it for a test drive and it felt good, a little under powered when you start moving but once you pick up speed it had good acceleration. I have tried 525i manual and auto just b4 this and they also felt heavy when slow. The asking price was reasonable for the condition of the car, after discount it was even more reasonable. Next day took it to a well know bmw shop for a check up, they did less than I expected, reved the engine, listened, then lifted the car looked underneath with a torch light, checked the exhaust, that's about it. They asked about the price that i was paying for it, they said I may want to get a new exhaust because the cat is not good, but other than that it was good. I payed the 80 bucks inspection fee and off to puspakom.
I'm worried about future maintenance cost, but heck it is a very nice ride.
Good luck in your hunt.