So basically let's just say you have 30 performance points and you can use them on whatever you want... just when your run out... your out. It's not enough to fill up all your stats so you have to pick and choose? I can dig it. I know there are some games out there that have done this but heaven forbid for me to be able to remember what they are right now.
That being said... I still think that the vehicles should still have their own distinctive underlying stats. That along with while you can apply these points however you wish, they should be limited in what they can do. For instance, I wouldn't want someone to be able to upgrade a lightweight racer to the point that it just ends up being a driving tank that can bend the laws of physics with its stock speed and grip. These upgrades need to be kept within reason.
This also brings in the possibility of race classes from stock, or lightly tuned to an unlimited class or something (not really unlimited) where before each race you could kit out your vehicle with the amount of points that are available for that race type. 0 for stock, 10 for light tune, 20 for tunned, 30 for ballistic, 100 for unlimited because screw logic I wanna go light speed and be able to shrug off ICBM's like its nothing.