Not sure how much weight diff there be. The standard covering is the inner skin/wall, foam then an outer of ply with the alloy on top. The glass one the outer ply is replaced with the vinyl/glass skin. We are only talking the side walls, the front and rear are already composite. I find the alloy great to wash, always shines where as with the expanda if you missed a bit it stuck out like "dogs" the alloy is also easier to repair but probably easier to damage .
I don't think I would have a problem with either, other than no way would I pay another $2-2,500 more to have one over the other. I think they'll run this for a while and get a few wood ducks paying the diff, when that dribbles out theyll make it standard on the SCs and marketing will use it as some great "2016/17 model improvement , $2,500 value free" blah blah