Unlockables:
Colin McRae R4 Bonus Car
Finish in first place in all 66 events to get a 100% completion.
Ending videos
Finish in first place in all 66 events to get a 100% completion to unlock two ending video sequence.
Hints:
Speed Increase
Increasing your speed can be pretty easy: with a Toyota Tacoma (recommend, but not a must) go for Hill Climb, Windy Point A or Pikes Peak BC. These are almost straight routes.
CORR Rallys
In order to avoid the pile up at the first corner, you can let all other cars pass by you when race starts, and only accelerate afterwards. Might offer you a huge advantage.