Things to have around. I like to keep some clutch bearings, shoes, and springs(I use Mugen Stuf). I broke an axle once. I also keep a bag of assorted rod ends and control arms, but never used any of that stuff yet.
Upgrades? If you dont have a pro version, replace brass bushings with bearings. Mayhem St chassis stiffeners are nice looking and do a much beter job. I also use the stock steering servo for throttle/brake and upgrade the steering servo. That should get you going....
Oh , and in the summer I had been to Venture and they had nothing for the mayhem. Ive ordered alot of sportwerks stuff from Als and they always seem to double my order for there stock. They have a large selection now.