Most of the CAI are really only worth it , unless you go with a full competition exhaust along with it and a good remap.
Already well covered in this old posting
http://www.the370z.com/nissan-370z-g...-hp-gains.html
For every day street use they aren't really worth it and you will only sense a little more intake air noise and a louder exhaust if you change both intake and exhaust.
The expensive intakes are really for the little posers that gather at the 7 elevens with their hoods up and say look at my chrome pipes and neon LED accents.
For the money your better off putting any money into future brake,tire or handling packages, most Z drivers will trade their cars off in 3-5 yrs. so its not really worth it to put a lot of crazy mods into it, you never get a return on them, when you sell them off.
Also a bone stock, unmolested 370z will bring a lot more at trade in time, smart buyers avoid all the cars listed with the Bad *** sales pitch and crazy amount of mods.