I've said this before but I think it's worth repeating:
Installing fancy top brand oils, plugs, intake kits, and other whiz bang gagetry will not significantly effect your mileage. It may not hurt your X, but depending on how crazy you get, it will hurt your wallet.
Economy and performance are typically opposite ends of the spectrum. Your X was already designed by engineers trying to maximize efficiency while still maintaining enough real world performance to make the X useful as a small SUV. Installing an aftermarket intake system or filter will have no appreciable effect at anything below full throttle, and the on board computer will adjust everything accordingly to maintain the proper fuel air ratio. More air in = more fuel in. Intake restrictions are really only an issue when it comes to maximizing horsepower, not economy.
There is only one thing in the intake system that you can change that will have any noticeable effect, and that is the position of the throttle plate. Control your foot, and your mileage will be better. It's easy and free. I can easily get low to mid 20 mpg on the highway by keeping it around 60 - 65 mph.
Go confidently in the direction of your dreams! Live the life you've imagined. As you simplify your life, the laws of the universe will be simpler. - Thoreau