[Ashlandchris]

Not sure on exact spec of current tr02 rtr, but if it is similar to when I bought one for my son 2yrs ago, heres my advice:-
Replace bushes with bearings. Cost ~£12
Keep an eye out for some big bore shocks - typically 2nd full set for ~£25 (you might need the front turnbuckle ball cup to be replaced with one for big bores - think they cost ~£3 for a pair)
Replace the turnbuckles with a set that can be adjusted with a turnbuckle tool rather than pliers.
Any breakages, replace with the "comp" spec plastics as it has slightly more carbon content and I found the front arms lasted longer by spending an extra £.
Finally, locking hexes for the wheels as the plastic ones slip off the pin and you then lose the pin...
Car drives well so in my opinion, there are plenty of things to spend money on, but none are essential.
Oh, and get a spare screw for the ball diff (think it was an odd size like 2.5mm *40mm) as I have seen 2 people snap them and it isn't a common spare