Romio, You pose a good question, that I don't know if anybody has actually tested out.
Since the spoiler creates down force, I would assume it causes a certain amount of drag also. So automatically, you would think with drag, fuel mileage would be effected.
At lower speeds, I wouldn't think it would make any difference at all, but on the highway it probably could.
Of course the only way to render the pop up spoiler inactive is to pull the fuse, so that would have to be done before checking the cars gas mileage.
If anybody is planning a little trip in their Limited Crossfire any time soon, why not perform an experiment by checking your gas mileage in both directions, but disabling your spoiler in one direction.
I realize there are other factors that need to be figured in like wind direction, average speed, elevation changes, temp. etc. But maybe we could come up with a "ball park" figure to go by.


(Legal Disclaimer) Disabling your pop up spoiler could possible cause one to experience an unsafe driving condition while driving your Crossfire and should not be performed under any circumstances. No one at Daimler/Chrysler, Crossfireforum.org, or private individuals there in, authorize such conduct. To do so, would infact be an act of disregard for personal safety, and thus be construed as doing so at you own risk.


Now, with that being said, and this being a free country, Let us know how it turns out.