Well I haven't noticed any real problems with screen tearing or slowdown but the game seems just as dark as it was the last time I played it. And yeah, there's an arcade mode so you don't have to stick to the mundane career mode of having to play that lame ass high speed ring over and over again, so it's not just sticking to your lines. You can play high speed bumper cars all over the world.
BTW, I checked the online manual and evidently you can unlock Quick Tune after completing all the events in A, B, and C Classes. So I was wrong about the actual car tuning....which you didn't care about anyway. :p