Dang. That almost pays for the tune in the mileage savings.
Using rough numbers. For the sake of easy math. Cause I suck at it...
I average about 25mpg all said and done. We'll call it 35MPG average that you're getting.
10MPG additional over a tank at 12Gal a tank (cause it's never completely down to the 13.2 gal cap) means ~120 miles more per tank per week if I fill up about once a week. That's about 3 1/2 gallons saved a week. At $4 a gallon that's about $14 saved each week, or around $50 a month.
How much was the tune? For some reason e-tunez.com is blocked here at work so I can't check, but I'm guessing a basic package would be right around $200.
So the tune would pay for itself in roughly 4 months. Dang. That almost makes it worth it to go ahead and tune as I sit at pretty much stock, and then I could retune after adding more bolt-ons.