Think about it this way. You spend $350-400 to increase 1-2mpg.
Using 20mpg and $3.50/ gallon, and a length of 50k miles as baseline
50,000/20 = 2,500 gallons
2,500x3.50 = $8750
50,000/22 = 2273 gallons
2,273x3.5 = $7954
As you can see it takes quite a few miles before you recoupe the cost of what it took to get that small extra mpg. Which most of the time the way you drive affects mpg more than any "mod"
Bullitts are better than Bullets