Its not how much power "gained", but think of it as power "not lost" keeping temperatures under the hood lower especially from your intake brings in cooler air into your engine which should have more oxygen which will in turn make more hp.
I'm sure some of the other members can explain it better but thats the short and sweet version.
You won't feel it during everyday driving but it should help autrocrossing or on track days after repeated runs.
It wont make any difference, onyl if you have a open element intake with no heat shield llike AEM and K&N, all enclosed element intakes and other open element with heatshild i snto going to amke a differnece, is not going gain any power by any chance but it will keep the oxygen the car needs cooler which makes the engine better...its like would you prefer breath cold air or hot air into your nose? get it? i would prefer to spend that money on get rid of some of your weight so that your car will weight less therefore it will go faster... :lol: