I've done over $1000 in upgrades to my rustler. By far the best upgrade I did was the Aluminum Extended A-Arms. They widen the truck by 1/2 an inch and this made a world of difference in the handling and stability of the truck. Before with the 3.3 engine the truck was completely unstable, now its handling better then I ever thought it would. After this upgrade my next favorite has to be the high torque metal geared steering servo. This combined with an aluminum bellcrank set improved the steering/handling of the truck tremendously. Outside of this you should just see what you break the most and repair/upgrade as you go.