I doubt it. You can always wait for X box 360, and Forza 2. But heck, if I move to Huston, I'll send you $200 to help stay cool during August.
Muscle cars are tought cookies, but so much fun to drive. The classes are determined by a power/weight/handling combo.
Thus it is way better to have a 300HP, 2700 lbs Subary like riding AWD on 235s than a 450HP, 3700 lbs Challenger riding on factory 215s.
... But, contrary to GT4, you can drift, so those pre-1975 championships are a blast, yet rare since easy mode LA7s are always the favorites.
When you go to the higher street class, the Muscle cars are out of the game. A 900HP blom 68 Gto can't keep up with a 360 Modena, or a tricked out ricer with all the downforce. You can't put spoilers on muscle cars ... so when comes the turn, comes the wall.
And in the lowest classes, the muscle cars are too powerfull to be in them.
But they can hold their own in the B class (D C B A GT GTR P1), assuming you don't make any mistake and the ricer AWD is watching TV, drinking a coke.