I see good points here from Tom... and Metro. For the small stuff, you can do a corollary study to show a general (albeit small) trend that would not show up in the noise of an A-B-A test. One could argue that such small changes are not worth doing if not noticeable, but I noticed a general trend after removing my mirrors, roof rack, and modding my wipers. I couldn't get a coastdown or immediate, consistent A-B-A measurement of the gains, but they can't possibly hurt, and I generally improved by about 1mpg over several tanks after the three small mods.
I have absolutely no doubt that the front wheel skirts will help. If A-B-A was inconclusive with just one, there may be enough improvement with both to see a small trend emerge from the noise of testing results. (plus, it looked sweet!!) Also, it might be worth waiting until after making the new air dam - with more air pushed to the sides and over the top of the car, the front skirts become more important and thus more noticeable to get full gains of the air dam.
That said, this has been a bit threadjacked - when are we going to see a "professional, true-factory looking" airdam appearing on Darin's firefly?
