Actually a short ram/warm-air intake will theoretically increase mileage. Warmer air is less dense which will cause a wider-open throttle plate and less resistance to the intake air. Now before the flaming starts, this is just my two cents. In the "real world" I doubt there is any mpg difference between a stock intake and an aftermarket CAI or WAI. A WAI will reduce your max power, especially on hot days....again, the lower air density due to sucking hotter engine compartment air.
The only suggestion I have for better MPG is using the recommended 5W20 oil, and increasing the tire pressure. Make sure you do not exceed the max pressure listed on the sidewall. A trade-off of higher tire pressure, however, will be feeling every bump in the road.