I don't think the M3 is a poor man's super car, and isn't intended to be. The M3 is a PRACTICAL alternative to a super car. I'm guessing many of the buyers have the need for the space, extra seats, clearance etc.... The buyer of the M3 is more motivated by practicality than price - in my opinion.
A ferrari would be largely useless for me, with two little kids and Minnesota roads. I could drive it like 3 months out of the year.