no idea of how many hours, though I'm in year seven now and for the first time about to have a shot at the KOTY-race.
Have to admit that I did drag the process of getting #1 a bit with changing cars to prevent me from being "too fast" through the game, but I didn't know about the KOTY back then, so ... heh.
If it wasn't for the 24h races in GT4, I would have spent more time in Enthu than GT4, I suppose ...
I've spent atleast 100 hours on Dragon Range alone....