No surprise here. Sure, the M2C has marginally better performances than the M2's (source:
http://www.zeperfs.com/en/duel5975-7280.htm and, for more details,
http://www.zeperfs.com/en/match5975-7280.htm), nice (optional) seats, and cooler mirrors. But the price to pay is huge: a significant regression in terms of aesthetic (subjective) and sound (not so subjective) combined to a castrated engine delivering its maximum power at 5250 rpm (M2: 6500 rpm). Yes, the M2C's engine can rotate up to 7500rpm, but what the point if the power remains constant from 5250rpm? At low rpm, the M2 is even more torquey than the M2C. From a financial perspective, the M2C is more expensive and depreciates as fast as the M2, at least here in Europe. And if, with the M2C, the goal of BMW was to put back the M2 well ahead of its main competitor, the TT RS, they clearly failed:
http://www.zeperfs.com/en/duel6234-7280.htm.
At the end, both M2s are still pretty awesome and fun to drive, but for a possible real improvement of the M2 concept, my 2 cents is that it's better to wait for the M2CS (if not too extreme nor expensive), or for the M2 2.0 and its promising S58 engine.
Now, for folks wealthy enough to buy an M2 only to track it from time to time, and who don't care at all about losing its warranty or about its residual value, it makes sense to upgrade to the M2C and its S55 easily tunable to >500HP and with excellent cooling performances.