tl;dr I like rewind and racing lines, but I do worry about whether I rely on them too much and can think of some ways to wean people off them more forcefully.
If you're just asking me if I think the racing line/rewind features should stay or go, of course I'm going to say stay. Racing line I can kind of take or leave, but rewind is the difference between "oh crap how am I going to get this turn right" and "FUCK I JUST WASTED TEN MINUTES ON THIS FUCKING RACE FOR NOTHING." You still have to be able to MAKE the turn, even with rewind.
That said, I have felt a bit of creeping in games like Forza. In Gran Turismo, I tend to turn the racing line off; usually the crutch I rely on in GT is the indicator telling you what the ideal gear should be. In Forza, though, I tend to leave at least the braking line on, and I rarely think to go back and turn it off later. Rewind I always leave on for the above stated reason.
I think people just don't want to feel like they're wasting their limited time. If I need to win a specific race to progress, and I spend an hour without those features and just can't hit the apexes or misjudge the grip on the final corner of a ten-lap race, then at the end of it I have nothing to show for my effort except maybe marginal improvement in my times that the game doesn't care about. If progression isn't as tied to having to win absolutely every race ever, then that improvement can be rewarded in other ways even if you didn't win, so you don't feel so much like you wasted time. So I'd probably start with making progression less tied to coming in 1st in every race. Forza's already pretty good with this.
DiRT Rally is also strangely good with this (or at least it was in early access), even though it's a pretty hardcore rally sim. Even though the game is still about trying to beat all the championships and whatnot, the game's a lot better about building in an expectation of failure. At first, half the battle is just getting across the finish line without pitching your car off a cliff. Unlike, say, Gran Turismo, the sting out of not finishing 1st is pretty small because of how difficult it is to put a great race together when you start out.
The other thing I think needs to improve is that games need to offer more incentive to turn off aids. Again, Forza is pretty good in this department, where turning off aids translates into increased XP and money to buy more cars and unlock events faster. But it could go a step further with this. For example, Forza Motorsport keeps track of when you make good/perfect turns. In the same way that Forza will eventually suggest that you increase the drivatar difficulty for additional rewards, it could do the same for the racing line if it notes that you're getting pretty good at hitting a fast line or judging braking distances. More gradations in the number of rewinds available, like DiRT used to do it, could help too. For example, maybe 0% for unlimited rewinds, +5% credits for three rewinds, +10% for one rewind, +15% for no rewinds. (15% is probably too high but you get what I mean.)
Something else that might be smart would be to have that kind of adaptive aid on a per-vehicle basis. For example, I probably don't need any help racing a Toyota Yaris around the track; it's a pretty slow and forgiving vehicle. But jumping into a Pagani Zonda R immediately is a recipe for disaster for newbies without something to tell you "HEY DUMBASS BRAKE HERE." A lot of the gameplay cycle in racing games is buying a faster car, then figuring out how to drive it, then racing to victory enough times that you can afford another new car. One of the reasons why I forget to turn off the braking line is because braking distances change based on your car and the environment (wet/dry, for example). If the game were smarter about suggesting I turn that stuff once I've figured out a specific car, I'd probably spend less time with the line on.