I think the guys who bought it as an "investment" are in for a surprise. Much like the guys who forked out insane amounts of money for the M4 DTM and GTS , and now they can be had for half of that
Could go either way though - look at 1M? I'm always weary of the "investment" car buyers. The truth is, cars are never a great investment, even the likes of a 250GTO since new has only marginally outperformed the S&P500 (probably under if you take into account insurance and maintenance and storage). And certainly no car has, on a risk adjusted basis, outperformed the traditional 60-40 stocks and bonds portfolio on any meaningful horizon.
If you bought an M2CS, enjoy it, drive it, if it's worth more in 10yrs time than you paid, awesome. You had a cool car, drove a cool car and maybe didn't lose too much cash. Much the same with any Porsche etc. etc.
Having test driven an M2Comp though I can't see why anyone would drive that and think "this isn't fast enough". It's absolute lightening, makes the Z4M feel postively slow. The only thing the Z4M has over the M2C is the sound and the look (and even that's subjective, I think the M2 cars all look absolute mustard but prefer the drama of the Z4).