you wont notice a huge difference in weight, i just put quite a bit of GPM's stuff on my tt01 and all the parts combined didnt weigh much more than all the plastic ones i replaced.

advantages of aluminum are stronger parts of course. this way you hopefully spend less time on the bench doing repairs if you crash and of course it looks much nicer. some food for thought tho is to leave some pieces plastic, if you do smash a wall going top speed you are much better off if your car still has some weak points for plastic to break instead of no weak points which would cause your aluminum to bend.