Keep in mind, wheels don't have an even weight distribution from the hub to their outer surface... most of the weight is on the very outer part of the wheel.

I didn't go through your math completely, but I think there's something else off with it -- vehicle weight shouldn't be a factor at all. The reason why reducing unsprung and rotational mass helps the car isn't because it makes the car lighter, but because that weight (both unsprung, and more importantly, the higher mass at a distance from the hub) impacts significantly the drive train loss. (Some percentage of your total engine output has to be used to both pass energy across your suspension to the body of the car, and to accelerate the mass of the wheels)

Boston Audi Group Website