well, aluminum is lightweight, but heavier than the plastic peice id presume. stainless would be heavy as a pig though, but would add wieght for traction for the winter
be more for show than go though, so if you're worried about every ounce of HP, it probably wouldnt be up your alley.
personally, i wouldnt want one, but id still like to see it. id rather the gas tank not be noticed at all than having it a focal point. could look cool though.
whats the name of your shop? i work for a sheetmetal shop in MA.