My personal adjustment for this current XP system is to earn credits each time you level up your car, something like 500 CR per level and 5,000 CR every 10 level. Even beyond level 50, the level bar repeats itself so you can still earn the in-game credits.
And also the ability to pay with credits when you didn’t unlocked a part yet. This will encourage you to level up your car and being careful about your own economy!