I've upgraded my RTR XXX-T for full graphite since I've owned it. I broke more plastic pieces and that is the main reason I upgraded. I figured since it was broke might as well upgrade.
If I were to add anything aluminum on my XXX-T, it would probably be the front and rear pivot blocks and maybe the rear hubs and front steering buckles. Thing is, you add alot of aluminum and hit something really hard your gonna bend the aluminum and the initial shock of the impact will probably break the plastic or graphite parts connected to it. Might as well break one part rather than replacing a bunch.