Hi, I have a 8v gti, 116.000 on the clock & it does about 35mpg on an average trip, 40 mpg if I'm on a run. Those figures are off the multi function display, not worked out by me, so I guess they could be a little off.
14mpg is likely to be binding brakes, desperate need of a service, faulty reading etc.....
In relation to the wings, I believe they are the same and that you can refit the arches etc