Extended chassis - CNC hex's - I kept breaking my top plate so purchased a BCE one - Shocks (See thread in truggy section re Revo/Jato shocks for front and Buggy shocks for rear)
The servo saver is the remaining weak link - I moved my turnbuckles to inner holes and have had less of a problem since then...
There are a ton of CNC parts ofna sells, but they aren't cheap. Good thing is they generally aren't needed. The truck is pretty tough out of the box. The one upgrade I did get are the 7075 CNC chassis braces. I launched mine off a giant dirt hill bashing around one day and fragged the landing right on the wing. The plastic brace bent and so did the rear dogbone. Luckily nothing else was damaged. Nitrohouse has them cheapest for $30 or $35.
I don't like beating the crap out of my trucks, but it has taken a pretty good unintentional beating since I got it and almost nothing has broke. The only really weak spot is the servo saver, but I moved the ball studs to the inner ackerman hole (after Arct1ks advice) and so far so good.
Edit:
Oh yeah don't forget the big bore shock mod. The stock shocks are crappy and small. Go-Ride has a good thread of his mod in the truggy section w/ pics. That's only $30 or so as well. The extended chassis is standard now IIRC too.
I'm going to run revo shocks so my suspension should be good to race. I'll look into those chassis braces even though I am not planning on racing I want to keep the easily broken parts on hand with the lhs not having the parts for the .5 in stock.