Sorry if this thread is too old.
Personally, I would lower the redundancy in event selection.
Beginner League should be Sunday Cup + themed races.
Amateur League should be Clubman Cup, Manufacturer races, open-class tuned, engine-based tuned and region-based tuned.
Professional League should be open race-car class and region-based race-car championships.
Random prize cars would be done away with. At its core, random prize cars is just an artificial way of making the game longer. Grinding should be left to old-school RPGs.
Speaking of prize cars, I would rotate them better so you don't end up winning the car you're obligated to use most of the time.
As for secondary features, I would add the ability to purchase a new paint job based on its manufacturer choices (a 32-bit paint shop would be nice but I assume it would be much harder to implement)
Then, because of engine mileage, I would allow engine refreshing for a fee. This one is especially important since you only win prize cars once.
I'm still on the fence on whether or not the starting money should be upped a notch since there are few relevant choices under 18K for a decent starting car.