My initial question would be what brand is it? Cheap filters = poor filtration. There's no issue with fitting a filter in place of the air box, on a dyno you would probably find it will have lost you some power?
Mishimoto intake hoses, fit duel throttle body 350z and 370z. Only been on the car for 6 months.
Smooths the air flow and looks allot better than the standard hose.
£60