Since I've never lived anywhere but the US, it's strange to think of these cars as being foreign, but seeing how many of you are European, it would probably be odd for you to think of them as domestic. I've grown up around these cars, and I've learned to revere them as part of our automotive history, as I'm sure our European brothers have their Aston Martins, Lancias, and Audis.
Speaking as an American, these cars are special to us. They represent individuality and expression, power and elegance...it's hard to explain. Muscle cars in Live for Speed would be an excellent addition, (speaking for myself now) and would make the experience that much more fun.
However, to add these cars to LFS would present a problem. Under the current physics settings, these cars would be nearly impossible to control, given their astronomical levels of torque. Imagine the RaceAbout, with twice the torque and the body roll to match a Spitfire. Not a pretty picture. If the grip problem that seems to plague many of the rear-wheel drive cars in this sim could be eliminated, then I think that muscle cars would be an excellent addition to the garage.