I agree. If you get a vintage piece, your getting a lot of headaches. On any given day, I'm doing preventative maintainence or repairs on at least 1 or more of my synths. But if you think you'll be seriously into synths, by all means take the plunge and buy a vintage piece, and treat it like a lady
I think
the Alesis ION would be an ideal candidate. Lot's of knobs, and controllers, sweet sounding, with a synthesis architecture large enough for you to learn a great deal. alternitively if knobs and sliders are your thing, you could also try to score a used
Roland JP-8000 (Definitelt fun to play if even not the best sounding keyboard) or
a Korg MS-2000(B). Both are available as rackmount modules too (JP-8080 and MS-2000BR respectively).
Personally I don't like rack modules in a live situation. I want knobs in front of me, because that's where my hands are I don't want to have to reach over to a rack to tweak a sound in the middle of a performance. In the studio it's not so bad though. So if you go rackmount, you might consider a module like the Roland JV series, and get a good controller (At least 49-key, better if you can get 61 or 76, or if you want Piano action an 88 key weighted). If you want cheap with decent quality, go with a M-audio controller. If you want a great board consider a Novation controller.