Originally Posted by SouthArk370Z

I'm no expert on modding 370Z engines. Most of this comes from what I've read on this site and others, plus some experience with "classic" Muscle Car era engines. YMMV

Nissan is already wringing out most of what the engine is capable of doing at reasonable cost and still be reliable. Most mods will give, at best, only modest returns. Any mods that make an appreciable gain in power will be expensive (well above your $1k budget) and have a negative effect on reliability.

Also keep in mind that the engine control system is pretty high-strung and many mods will make a re-tune necessary (or at least desirable). The more mods you make, the greater the need for re-tuning becomes.
You can probably get away with HFCs or CAI without a re-tune, but probably not both (not real sure about this one, maybe someone else can confirm/deny).

Most of the mods that increase air flow (eg, better flowing exhaust) will only give a boost at higher RPMs and can decrease power at lower RPM. Great for the strip/track; not so much for a DD.

For me, all the above means that engine mods are not worthwhile unless you are racing the car, especially for someone on a tight budget.

All that said, if I were going to drop $1k on engine mods, I'd go with the best sounding exhaust system I could get and a tune.