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motogp34, there are wings, and there are spoilers. Wings generate downforce, paying the price for that in drag. Spoilers are designed to smooth or alter airflow. In this case it's my guess that the spoiler on his trunk is where the airflow from the roof (and possibly sides) of the car is reattaching, providing a clean separation point from the car, which is desireable. Removing a well-designed spoiler can indeed drop the mpg.
As far as the vortex-related add-ons for the edge of the roof, there's been testing on this board that, at the very least, has indicated that it's very likely one needs the accuracy of an electronic MPG readout and cruise control, plus plenty of A-B-A-B testing, to determine if they do anything at all. I'd recommend getting one and hooking it up, like the ScanGuage II, or the MPGuino which is more hassle but far less price. It'll help you test each and every mod you get in a more accurate way than is possible by keeping track of fill-ups.
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