definitely want: HPI sway bars, graphite upper deck (w/ receiver pack), fiber brake disc, racing clutch. HPI option parts has all the woven graphite you could use. Asiatees.com also has lots of aftermarket parts for cheap!!!
Try out some 31mm tires if you're bashing, i think they would increase control but I haven't tried them yet. The stock tires are only 26mm. Upgrading the radio system to 2.4ghz is an extremely smart idea to ensure that all these expensive mods stay protected.
Remember that gearing up only makes it faster in a straight line
AE B4.1 Worlds, Losi XXX-T CR, Tamiya F104, Jammin x1x, HPI rs4 evo+