ok, as far as plugs... Better spark, so maybe slightly better power, but w/ out performance wires(8.5mm) not too much.
Air filter... if you were to dyno your car w/ that k&n system on, you would prolly see a HP gain of 1-3 HP not a ton, but its a great place to start modding w/ a N/A. it does give the intake a much throatier sound. when u get on it you can hear it sucking air... but as far as overall volume.. its not gonna make it a ton louder...