i agree. to add:
little two plastic vents help (they deliver colder outside air, versus hot under the hood air.). there are two, the one you mentioned, and another sandwiched in the middle of the headlight unit.
my bigass cone filter (afe, bought at bavauto), replaces the stock airbox, and kooks up the plastic vents. heatshield protects it from the engine side.
gains i feel are indeed minimal, but felt mostly in the middle rpm range, 2000 to 4000. sounds is unbelievably awesome, i am ok spending $400 just to hear the roar...