I am not a pack rat, I just keep things I know I will use.
As for the pay back time, it will depend on how far I drive. With all my mods I am getting at least 2.5 MPG better. That is a change of +5% min.
All my mods cost my ~$45 to make (most of that cost is paint). Testing also adds another ~$28 in gas. All in all it will take a while.
I need to do some more testing to determine exactly what all the mods gain me. I have hard data (short runs but something) that show a .4 to .66 MPG gain off of the wheel skirts. The Kammback coast down numbers show a 2% aero gain (or about .5 MPG). I also did an upper grill block and a side mirror removal. Each of those is helping but I doubt that they both add 1.5 MPG. So I know that my testing numbers are a bit low.
I might find time this week to do some more testing. If I can only do one set I think I need to do a stock and full mods. I want to do each by them selves, but it is hard to justify 2 hours on each mod + all of them
http://forum.ecomodder.com/images/smilies/mad.gif It also costs me 1 to 2 gallons of gas for each test (to get a valid data set) or about $5 a test. So is $5 and 2 hours a test worth it?