I loved those games. I bought 3 versions of the games throughout the years. It was a lot of fun buying and tricking out cars. I usually always started with a Subaru Impreza WRX which gave you the best bang for your buck in the game. Much cheaper than doing it in real life.
Real Sports did a piece on Lewis Hamilton, one of the top F1 drivers in the world (Actually, probably the best). He practices on the Project Cars game, same thing as Gran Turismo. His brother has CP and he learned to drive on the same simulator and he's currently racing in one of the smaller British leagues.
I've also seen Nascar drivers using a simulator to learn tracks, even Tony Stewart did an exhibition where he drove an F1 car, so he practiced on simulator.
If it's good enough for them, it must be incredibly real and an incredible learning tool. The rig looks expensive to have a real setup, vs. your typical controller or generic video game wheel and pedals.