This link is an example only of a car with almost 100,000 miles. Let's assume it has been maintained, updated, no major issues, no tracking or thrashing, etc..
Since before I bought my M3 I looked for anything I could find about the cars. One article quoted a BMW engineer predicting customers could expect 200 - 250 thousand without any transmission or engine problems, he based his comment on BMW reliability in general, but BMW engines that get awards year after year do so for a reason. Just saying.
Is 100k miles halfway? If you were selling your M3 with 100,000 miles on it, what would you tell potential buyers about longevity?
http://www.autotrader.com/cars-for-s...49152476&Log=0
Pretty cheap for essentially, no, exactly the same thing you get new today for $80,000.