Upgrade parts would strike a better balance in wheelspins—they are underwhelming enough that receiving a car or credits still feels more exciting, but they are still useful in order to save credits as you progress. The logic of the common–legendary range can easily be applied from street upgrades to race upgrades, and having these banked in your upgrades menu also makes building cars more enjoyable and less repetitive. Exclusive paints or vinyl shapes only available through wheelspins could also be fun.
While clothing and emotes can be fun to customize, not everyone bothers changing them. But virtually every player will interact with the car upgrade features. Clothing and emotes make more sense as incentives to complete specific challenges, or to buy with credits, as is already the case.
Savings on upgrade parts will lead to a fair increase in credit balances for players who come back consistently, and make it easier to save for more exclusive cars, houses, etc.