all honesty if u plan or racing save ya money.
sure buy new packs (anything with east power or intellect batteries) these u can re solder for a new chassis but i dunno bout ur track but at mine anything less than an rdx or mi2 and your kinda pushing your luck to win,
so if u plan to race batteries tires and a 2nd hand chassis.
drifting on the other hand as far as i know there guys like a rear spool(lock the diff) and either a front spool or oneway then adjustable upper arms and steering links. they dont really go all out like racers.
but the most important things are batteries tires and motor tire are prob the most important. so make sure u got these right before u buy that flash radio servo or charger, trust me a $400 is really no use to u when u have no grip