I have a baja champ. The ball bearing set for a TL-01 costs about $20 and really turns the car into a better runner. That's the only upgrade worth doing, IMHO. The fact that the battery pack sticks out the sides makes this a poor choice for off-road fun.

The Evader series or an Associated buggy kit might be the ticket for your next ride. You can pick up some deals on Ebay on "last year's models."

Regards and good luck.