Well OK they do improve one tiny bit near the end and hence one final statement - don't attend a race without completing the previous one in 1st place and upgrading.
It is retarded in a way, to beat it you have to see exactly which - keeping on the track doesn't matter one bit and you don't have to go between the markers, just pass within a reasonable range. The controls and handling are still crap and don't really improve...
 "Fishing Girl"){kind=icon}
 "SandStorm Racing"){kind=icon}