I used to hardcore grind the big 4 races.
Tokyo 600 - 3K times
Sardegna 800 - 1K times
Spa 800 - 500 Times
Le man 700 - 1K times.
I was on a mission to get every car in every color/livery but I hit the wall that's the 2K car limit and so that dream was dead.
So I switch to buying X20 for each of my favorite car. I finally finish last year and so I stop grinding and now I just have fun in custom racing.
The only cars I'm missing are the few PD has added in the last few updates I can buy them at any time so I'm not in a rush.
Last since I been accuse in the pass I done all this legit no afk or auto grind some find it hard to believe but I enjoyed grinding.