After installing the v8 box,tubes and K&Ns my ultraguage readings for the MAF increased across the entire RPM range. More air = more power, this is fact. The engine can and will take in more air in than the stock setup allows. You are making the assumption that the stock air box is able to flow more air than the engine could use and without restriction. Changing out the stock filters alone will prove that to be false as you will get more air. Step up to the NW dual on an NA and you have an argument, that setup has the capacity to supply more air than the NA can use effectively without mods.

While I admit dyno results for an NA with only a CAI and no other mods is hard to find there are still some out there. Searching needswings intake dyno in google will give you a number of results for crossfires and other mercedes v6. The supercharged versions see more HP from the mod than the NA but it is still a good amount of power/$ considering the few options we have.