Plenum, induction kit, hi flow cats or decats, exhaust. But even on a standard car some power will be found, it will be better on fuel and will have better drivabilty. TBH its about what you want and the Uprev reflash will make the best of what you have. I think anyway.
I wouldn't bother with an induction kit personally. Stick with the standard induction and get a free flowing panel filter for it. Most, if not all induction kits will lose you a few bhp.
sorry I may be misunderstanding you, but why would nismo design an intake if it's going to lose you power? Now meaning to be rude but just wondering what's the point of them then?
Very good question! I have no idea why they would do that to be honest, but a cone filter which is exposed in the engine bay (such as the Nismo one you mentioned) will never be as good as the standard induction which has a properly sealed box. Cone filters will always suffer from heat soak. Found this out myself the hard (and expensive) way!
I guess people buy them for the noise and the fact it looks nice, I know I did!