I think the MPG change would be more due to the wind resistance, than the additional weight.
VT maverick, if you are really close to getting into the garage, you may want to check out member zeus's ride. He reversed the rack mounting clips, to lower his rack a few inches. He did it for aesthetics, but if you are close, it could be all the distance you need.
Wow, I've never heard of a hitch not attaching to the frame. Maybe that's why our rigs aren't rated to tow anything.