I'm not a racer, I'm a basher. As far as lightened clutches go, I can see how this would benefit racers a little.

As far as catching air and when you gun it to pitch the nose up to keep the vehicle level, the clutch is still engaged and the rotating intertia of all 4 wheels and the rest of the engaged drive train provide more than 10times the moment of enertia to prevent the engine from revving up too quickly. If the wheels run free like that too long (10sec+), then your conrod journal will suffer from permanent strain and expand and eventually snap. I don't know of any RC that has been able to catch that much air time though (If some one has, I'd love to see that!).