I am FAR from being a top driver, but I still feel like the lack of variety is absolutely bothersome. You hit the nail on the head. With 1200+ cars to choose from, it seems kind of silly to force people to drive the same cars over and over again. Frankly, I think this impacts the lesser skilled drivers as much as the top drivers. While top drivers must use a particular car if they want to compete for best overall time, the lower skilled drivers must use that same car if they just want a shot at getting gold.
Personally, I would prefer if they picked the car we had to use but allowed tuning. For me, that Seasonal Event Time Trial with the Lexus at Nurburgring 24hr track was an incredibly difficult event because my skill level just isn't where it needed to be to collect a Gold medal time. If I remember correctly, I was 3-4 seconds short of the Gold time limit. Shouldn't Seasonal Events be challenging like that?
Again, I would prefer if they allowed tuning, which they did not allow in that particular event at Nurburgring, but I think you get my point. This way we would all be taking advantage of our vast collections of cars, tuning would still play a major role in determining the overall event winner and average skilled players like myself would really have to claw our way to getting Gold.
As difficult to handle as the NSX is for me, I only improved my time by one second with the ZZII. The nasty vertical lefthander got me every time.
... Maybe some absolutely genius trans settings could help there at least a bit... 
