I don't completely agree with that, IMO they do make a difference, although I would agree how much is up to question. As an example just a cold air kit with no other mods might beworth 2HP, combine it with a set of headers and an intake elbow it might be worth 5HP, put a blower on it and it might be worth 10hp over a stocker with the same application. It also may be 10hp in one rpm area, and actually cost you hp in another. there's no "magic" number and unless you test each one on a dyno, you'll never know.
IMO I would recomend these guys New Page 1
Whatever you do I would make sure the intake pickup is not in the engine bay area, it should pick up cold air from outside somewhere and stick to a plastic tube.