I'll be in the market for an M3 in 2013 (used or new TBD) and this is very insughtful. I probably will have to scan through all the pages in that thread anyways - focused on year, body style, options, etc. But this is a great start.
Out of curiosity, did you get a significant R2? When you include the other variables, does the R2 improves significantly? On the more detailed analysis did you look at E90/92/93 separately?
I would definitely be interested in the results of the more detailed analysis. Should I pm you or you plan on posting some time?
I wish this thread gets much more views, because it really deserves.