My SC18 is running strong now. I probably have 10-20 hours of run time on it...not hard when the 2200 lipo lasts 40 minutes! Here are the improvements I made that I consider mandatory:

1. Replaced stock short shocks with RC18 long shocks (this will probably wear out your diff outdrives sooner...but makes the car so much more useable for off-road)
2. Installed NOVAK Mongoose 13.5 brushless set
3. Bored-out stock steel pinion to 1/8 inch to fit Mongoose BL motor
4. Implimented "Rosario-hole" in belt tunnel so now I can see pinion/spur mesh
5. Installed HS-65MG servo and and AE RC18 servo-saver for Hitec

Optional upgrades I have made:
MIP CVDs
Futaba 3-PMx (exponential and servo delay help a lot with controling these little cars)