RH77,
I autocross the TDI, may daily driver:
Autocross is really not too hard on cars... not as hard as road racing, anyway. I still find my car to be quite reliable. I just replace parts before they break. I've never tried Rally-Cross. Autocross is about as much competitive autoracing as I can have without a "conflict of interest" in my home.
It's the summers of autocrossing that really bring my FE average down. Sure, I just averaged 48.5mpg on an 1800 mile adventure in TN. But I'll also get just 43mpg during the summer weeks of commuting in DC traffic; and towing/autocrossing will knock my FE average down after a few trips at "only" 35mpg.
But I know FE would be much worse in just about any other car under the same circumstances.
Scott