Physics is not in the Spyders favor: with the big frontal area Spyders will never do as well as a two wheeler. BRP did tweak things on the RTS to improve millage over what it could have been. The RTS carries more weight, and has a bigger frontal area .... yet mileage is only slightly less than an RT. No doubt as gas prices rise, BRP will do all it can to improve mileage.
or

the Spyder could get "Aero-modded" like this?:
Aero-Modded Geo.. by a mileage fiend.
Note this quote in the article
"A participant at MaxMPG correctly pointed out that a single rear wheel design would have permitted even more body taper and less rolling resistance ... and that may be true, but it also would have taken this project well beyond a one-month "back yard" endeavor."