Depends on what you've done/are planning to do to the car, and naturally the intake and exhaust setup you choose.
A direct stock replacement drop-in K&N filter is obviously not going to be as high a horsepower gaining "intake" like a full CAI system will be... same as slapping on an Auto Zone muffer isn't going to give the gains that a Borla cat-back will.
Like bink0r said, some cars REALLY benefit from a freer-flowing exhaust. Some RX-7s have insane power gains just from opening things up under there a little bit... Rotaries love to breathe.
Anyway, yep. Depends.
