A cold air kit will help SLIGHTLY... but expect a decrease initially. You're gonna' play with it lots to hear that new "growlly" sound.
Looser (larger) exhaust will help SLIGHTLY also, but as with the above...
If you want good fuel mileage from your X, the easiest thing to do in buy another car.

These things are "Billy Goats the can't get past the hay bale".
Jeff!