I'll throw in my $0.02 on the E30 M3. I had a very low mileage '88 and it was a blast to drive but it was old no matter how you slice it. It was not an everday driver and I cannot imagine using one as such, although many people do. Mine was bone stock and yes, it did need part refreshed just from age. That S14 motor is wonderful but it takes a knowledgeable mechanic to work on it. Boy does it like to rev and the throttle response was instantaneous! Anyway, it is a super car but I would not recommend one as a sole vehicle and you do have to be prepared for bigger maintenance bills.
As someone else posted, good ones are pricey and the cheap ones are usually very rough. Non-modded ones are quite rare too. I would love another one that is in museum shape but wouldn't we all?
I think the best person to ask about them is inlacal. He has/had two of them and one that was absolutely cherry. I've seen them in person at some BMWCCA stuff years ago. He's the expert on the E30 M3 for sure.
I think it might be a good idea to lease an E90/E92 328 with very few options. There have been some great lease deals on them and BMW residuals are very solid so you won't wind up owing unless you go over mileage. I leased my E90, my first lease. I went nuts and optioned it up too much though. Get one with ZSP and that's about it.