I would definitely buy it... I've come across a couple cheap e32 V12s but I'm still going to school and I already have 2 cars, nvm a third one lol. I would definitely consider one in the future though. The m70 I believe is 2 m30s put together. Its BMW's Frankenstein of motors lol. And yes it is expensive to maintain from what I've heard anyways. Then again they say the e32 V8 is expensive to maintain, yet its only cost me about $500/yr and I do all the work myself too. The only thing I would really advise to be careful with is the self leveling. That can be very pricey to fix, but there are delete kits for it too.
My e32 is an absolute joy to drove. Even for an old car, it gets a load of attention and it has that aggressive but classy look.
1997 BMW 540i/6 sport
1984 BMW 733i E23: Centra staggered 16" rims, Hartge strut brace, Hartge engine
1994 BMW 740i E32: Sold