I think I know which stats are more important than others (at least most of them), but I think the stats should make more of a difference than they currently do. In my league, my drivers' graphics look a lot better than those of some of the other drivers, and yet their performance seems to be usually equal (even with a similar car)
For example: This is one of my drivers - http://igpmanager.com/play/?url=team-driver/20701
Compare that to this driver - http://igpmanager.com/play/?url=team-driver/14015
By the looks of it, you'd probably say that the second driver has better raw speed, but Santiago should be better at everything else, especially being level 14 compared to Hamilton, who is level 11, and yet there is very little difference in performance.
Maybe not having a high mental should increase a driver's rate of health decrease, and attacking to defense ratio should be better. Also, I think setting up the car should be made harder, to make people train the technical. Because even with poor technical stats, it's easy to get to the 'feel good' stage.
Just some suggestions anyway, because it feels like there is little to no benefit in training some attributes.