Admittedly I didn't read through 19 pages of posts so my apologies if this has been said already.
I'm an American and by NO means a NASCAR fan. However, if Gran Turismo is going to tout itself as a driving simulator covering all aspects of racing then yes, there needs to be at least 1 or 2 famous American oval tracks in the game as well as a few NASCAR vehicles. Indianapolis is home to one of the most famous races in the world; someone explain to me how that track has not yet made it into the GT arsenal?
Indianapolis and Daytona would make excellent track additions because, while being ovals, they also have good, technical road courses. Indy is also home to the F1 USGP, and Daytona is home to the Rolex 24hr endurance that sees teams from around the world. Those are two major tracks that IMO are far more famous than Infineon.
Road Atlanta is another outstanding American track; a very demanding road course that's been a famous American track for years.
And while my info on Australia is limited, I would very much like to see more cars & tracks from there as well.
Obviously Gran Turismo is biased towards Japan but let's be realistic... if Polyphony Digital wants to hold the title of driving simulator as well as a historical representation of autos and racing on a worldwide scale then we need to see the tracks I've mentioned.