I'd say the market exists, but you've got to convince people the price of your kit will be recouped in fuel savings down the road.
And you'll have to convince people that the kits actually look good. This is the major hurdle. Sell people a $2k set of flashy chrome wheels that'll kill their fuel economy and will cost them many thousands more in higher-priced tires to fit their new rims... and they won't bat an eyelid. Sell them a fuel-economy improving body-kit that makes their car look like an Insight... and...
