[Richbot]

Figure a nice example with good service history will never cost less than about $15k, probably in 2020 or so, after that the nice ones will become more and more rare and start to be worth more and more money (though certainly not ever "barret jackson record-setter" money). Anything less than that and you're probably looking at extremely high mileage or needing lots of work or both, not that high mileage necessarily means bad car. We're already seeing this with the E46, go find a truly "mint" condition E46 for less than $25k, I bet you can't (I couldn't, I looked)

But like the E36 and soon the E46, you will probably be able to find a much-less-than-perfect but still very usable car for less than 10k. Unlike the E36, it won't be cheap to fix, which means the price spread between a good example and a less-than-perfect example will probably be pretty big

For me, I knew the E90 would be the one that hit my sweet spot for a "perfect" car, so I pulled the trigger three years ago and I'll never sell it. For you, I'd wait and see what comes along in the next 10 years. The next two M3 generations are probably going to be pretty damned cool...