I don't have an issue with them offering this... as long as the cars prices don't sky rocket out of proportion to encourage paying for credits. If these are the same "prices" that were in previous games (this is the top car after all) and the progression/pay per race is the same I'm fine with it. There are hundreds of cars available + free DLC for even more cars.

If people want to pay to get instant gratification that is fine with me as long as the game is not created with "pay" in mind. It seems like in this instance (with the progression/gifts remaining the same) that this is just a option on the store for people with little time, that want to play with the fastest car(s).