In my opinion, assuming we don’t just remove Car Points, they should be tied to career events and not car levels. So when you go through a series, you are given a fixed amount of CP to build your car, regardless of car level. I have a whole theory on that.
But yes, with the current system, you’re constantly hitting the CP limit without really ever being able to have the build you want, and you really only ever get the CP budget to apply all the sensible race upgrades you want after you’ve finished a series.