Hmm, two points to ponder:
1. I realize that this thread could be interpreted as being about all "M" sized cars, but it really does focus on Tamiya product. Maybe it's time that there was a thread for "all other" chassis of this size? (or is there one already?)
2. I don't really understand the charm of the 4WD mini cars. They truly are, as Tony has stated, a slightly smaller touring car, with all of the complexity and p.i.t.a. that entails. The whole point of the Tamiya M for me is that they're dirt simple, have loads of slop, are durable, cheap to fix and just as challenging as any other class out there.
Throw in a carbon fibre chassis, drive belts and all the other stuff and the only thing it adds is "princess" factor. Ooh, I'm going to hear about that...