We've gone to the Race Rock twice. In 2002 and 2004. It is really centered around all types of racing from Nascar, Indy, Monster Trucks, Moto-Cross, ect.
If you are really looking more towards Nascar then I'd lean towards the Nascar Cafe in Citywalk at Universal. It is much better. Also, they usually have 6-7 Nascars on display.