My mpg's went up with a FWI, an extra 1-2 mpg highway, I get about 30 right now (not using the DIC mpg, I calculated it). A HAI (sitting right in the engine bay, not shielded from engine bay heat) will give you more mpg than a CAI or a FWI.

A power log (or plug for short) will give you some extra power and mpg for a good price, I'm still trying to find one used.