I'm not referring to that friction. Mainly, friction of the keyway interacting with the polycarb, and friction of the wheel interacting with the playingfield. I know our wheels got rather warm after matches last year.
Putting aluminum between the sheets of polycarb is a good idea. It may make your life harder, but it may be a much wiser move in the long run. One thing you could do, is put aluminum plates on each side of the wheel, and then use the polycarb as a "filler" between the two aluminum plates. Then you can make wheels as wide as you want with little weight gain, while still maintaining strength. Wider = better, traction wise that is. Turning may be difficult though.