I can't remember if you get full damage at lvl 20, or 40... In any event, I agree. They should let you turn it on from the start if you want it. I have other gripes with the game. The transmission is one of them. Others: AI is terrible. No Brake upgrades.
Gripes aside, I still enjoy its Gran Turismoness and will continue to play the game. I finally unlocked the Nuruburgring last night. I'll never tire of lapping it. The game is EASILY worth the $60 just to drive it. I also got some message that I unlocked a 4hr enduro at the ring (but as you mentioned, I don't know where to find it yet).
Have you messed with the track creator yet? I completely forgot about it until today. I'll have to give that a try...