Set Percentages

Upon playing the game completely through once more, I recognized that the credit amount given (subtracted from the total after the additional credits were added to my balance) after winning a car that I already had in my garage wasn’t anywhere near the total price of the car in the Autoshow. What percentage is used for the reward for duplicate cars given in the wheelspin? I’d like to know because I need to calculate how many credits I need to buy all the cars I don’t want to win in the Horizon wheelspin, granted if I win one, I’ll still get some amount back plus the VIP bonus, but does doing that help one win better cars on the wheelspin? I already have 3.1m credits and am only at level 48 (as of this play through) and the only car I want to buy is the '62 250 GTO. I’ve bought, fully upgraded and tuned every car I wanted to drive in the game already in previous plays through so I don’t know why I’d waste money on those when I’m already just a bit over half way to that point of purchase.

So, is the method explained above efficient? I assume it has its downsides and disadvantages, one of them being that even though you bought the car from the Autoshow, you still win it but can sell it for a fraction of the price (VIP helps a little) and saving up credits is my preferred method so far because I have yet to come across any other benefit that stands out when compared to saving up. But still, buy all the cheap cars, and progressively win better cars as you level up sounds fine. It worked for me until I restarted with VIP. Now I’m set. Anyone else do the same or have a different method of obtaining high-value cars?