Im not to sure on the mods that wont hurt, but theres something you can do that WILL help. I had all the mods in my sig, including the bcam (suposed to drastically hurt your mpg) and 3.08 gears. I was getting 12mpg. I went to 3.73, and decided i had to do something, i changed my fuel filter (it was stock) when i poured the fuel out it was BLACK, i changed the stock air filter to a k&n panel filter, and put fuel injector cleaner in it, and used sea foam. At the end of the tank i went from 12mpg to 17.5! I was extremely happy and get 240miles to a tank now ONLY CITY driving, car never sees a highway. If you havent done that stuff i would suggest doing it.

Wish I did that to my 84 240