I made all my aero mods on the red VX from ideas found here on Ecomodder and I did no math calculations. Because "maths" hurts my brain.
I am convinced that if you added some more aero from ideas on this site, you will see great results in your MPG.
I have picked up at least 10 MPG from what I did and I know some of it is "Down and Dirty" but still worked to some extent.
Also, any aero benefit you can add will always be helping MPG from now on, no matter how hard you may or may not be trying to hypermile.