Springs for tuning, and get the aluminum spur gear pulleys. Sorry, but the plastic ones in the kit are crap. I would also buy a variety of the small and large pattern spacers/shims, and the cone washers. You will use them for suspension tuning and shimming out the stock battery brace.
Speaking of which, you need 20mm screws for the rear most suspension mounts, and 18mm screws for the rest of the suspension mounts if youre gonna widen the car out to spec. Otherwise you will only have like 1mm of thread in the bulkheads with the stock screws. Thats spells trouble.
It also comes with a ball diff and a spool... so you may need to purchase a separate diff for the front... depending on your use.
For those that dont know... the stock balls for the diffs are NOT carbide or ceramic. If you plan on runnin some power... the stock diff balls wont last. My front diff was gritty after one run with an 8.5.
Im a little picky when it comes to my cars, so i dropped an extra $150 for parts on top of my kit cost. After 2 weeks... im still spending. You can run the car fine without the added expense... but there IS room for improvement out of the box. Conversely, im glad i didnt buy another XRAY.
As far as durability goes... its fairly strong. Its weak points are the rear hubs and the steering rack... as previously mentioned. In the past two weeks i have logged over 600 laps and broken one rear hub and the steering rack.
I have run the car waaay loose and reallly tight... both ends of the spectrum to find its capabilities... so it has hit a few boards, and traction rolled (just came off the track comin into the sweeper) and hit a concrete wall.