I can see why some people wouldn't want to allow cars of a lower class to run in the higher class. There is a huge speed differential. My ITC car would get killed by ITA cars, but at someplace like VIR, I was held up tremendously by an ITA car. I would get by and then he would drive by my on the back straight like I was standing still.

I think it is a good idea to allow lower classes to run the higher classes IF:
1.) you STRICTLY enforce the 120% of the leaders speed
2.) you run YOUR class letters in the rear window so it's easy for that ITA car to see you as they come flying up
3.) NOBODY bitches when the next higher class is already racing with you so you can't double dip )ie ITC and ITB running together).