I think that if you are going to do rear wheel skirts you may want to lower the front portion of them to the same height as your side skirts. Some other things (some mentioned) that will help would be kammback, disk wheels, tire spats, grill block (at least partial), underbelly (only if you dont have clearance issues), interior mirrors. I would also suggest that you install a vacuum gauge, to get instant feedback of how you are driving.
Many of these are on my list of things to do, though some may be a bit out of your comfort zone.
Here is a pic with tire spats, adjusted rear wheel skirts, full kammback and tire spats.
