To be honest, I could do without the racing line.. but I get why it's there, judging distance on a flat screen is much harder than it would be in a first person perspective if you were actually in a car, so it's a bit of a crutch for those that don't want to take the time to learn a track. Like I said, I could do without though.
The Rewind though, I like. It's not that I like rewinding every 5 seconds to do something perfect reconstructive surgery race, it's that if it weren't there and I made a big fuck-up, I'd simply reset the race. Once I get a track down and I'm trying to beat records or my own personal best, I will hamper down and keep playing until I do so... in the past, that meant if I didn't hit a corner the right way, crashed, spunout etc etc... I would be resetting the race over and over and over and over. The worst is when you have a race and you're killing it 95% of the track, then you get distracted or whatever.... boom.. reset.
So, if they get rid of rewind, I'd simply be resetting. With slow loading and shit, it is a major pain in the ass and a waste of time.