Jammin X2 CRT type fuel tank (snap-in mounts to route fuel line, markings on tank to let you know how exactly much fuel you used)with a Losi style clunk.
Tamiya style brake bias adjustment.
Top mount servo saver adjusting nut.
Losi style clutch (its nice having pre-built clutch set-ups ready to drop in)
Easy diff access.
Losi type air filters (how can you beat pre-oiled 4 packs for under $8?)
Nylock nuts for wheels.
Full set shock springs.
Full array of shock pistons, including blank ones.
Full set sway bars.
Instead of putting tires in the kit that many people will never use, why not put a voucher in the box for a free set so the customer can choose?
Mugen has a good idea with the Upgrade-RC body wrap.