why spend all that $$ on those expensive CAI tube thingys...?
but yes, if a CAI can direct colder air up into the intake pickup, you'll get slight mpg improvement. if your CAI scoops air and can pressurize the airbox slightly, then you'll get even better mpg, but dont expect a miracle, late model engines have a fairly high VE to start with, and getting more VE under NA is not so easy......
you might see better mpg gains by max'ing out your tire pressures ("max" meaning as high as you can go without abnormal tread wear, etc). my XRS gained 1.2mpg going from 30psi up to 39psi on the tires (30.8 to 32 mpg hwy).