I wouldn't expect to see any noticeable improvement in economy by changing the air filter to a K&E or some other type of free flow filter.
The greatest economy is had with minimal throttle settings where very little air is flowing thru the filter. This being the case, the differences in air flow thru the filter would not be noticeable to the engine.
The only time this would not be true is if the air filter was plugged up with dirt (or in the case of the K&E, over oiling).
Of course, everyone who installs a free flowing filter wants to see more power so it is pretty natural for them to "dial it on".