I wouldn't worry that much about rewind, as said above, you NEED in the end of the day to be able to make it round the corners, yes, it may result in dirty play, but if you're bad, and at the back, rewinding keeps you at the back, just not as far back as you were, if you bugger up that corner, you gotta do it again, you can't rewind the AI further.
Will I end up using it, yeah, I'm sure in a few events in the form off Fifa rage kicking in (Woe betide any man who suffers that!) but to be able to try lines, drifting etc.. it'll be invaluable, at the end of the day, it matters not to me if little Tommy down the road uses rewing every corner and 6 times a corner cause he can't drive for fudge, if he's that bad, he'll spin out first corner online, maybe taking someone with him then be at the back, if he continues taking people out he'd end up getting kicked, if he ended up getting kicked for punting people off the track, he'll learn not to, in the end, little Tommy will be able to take a corner without taking out 7 sheep and the shepard.
Its all a matter of skills, and these assists in particular, rewind will cater to all walks of life, from the skill-less, to the perfectionist, to the video maker, one button driving will help little Tommy or old Cyril who just want to race a nice car/car they owned in their younger years etc.. without having to worry about the physics that they don't care as much about.
It'll be different for everyone, I think too many people are really worrying about how others will play the game.