When I bought the game (day it came out in the U.S.) I played and played.
Eventually I made my way to 50% complete and hadn't sold a single car I won. Hadn't sold a single car at all. 👍
However, I wanted to unlock everything possible in Arcade mode. So what I did over the next 50% of the game's completition was sell everything I had, buy new stuff, use it one day, then sell it all off again to repeat the cycle.
Sure I've got every race car in the game unlocked in arcade mode (every jgtc, touring, LM, everything except 1 pescarolo) but I don't have much of that stuff in GT mode.
In GT Mode I've got plenty of race cars and pretty much all the ones I want but had I never sold my cars originally, I'd probably have every single race car in GT Mode as well as Arcade mode.
A blessing and a curse.
I've got all the racers in the game in Arcade mode but I had to sacrifice the GT mode cars to do so.
As I said though, I've made it out of that hole and I've got quite a nice garage now.