Take your car to stage 3, do some maintenance and make sure everything is working well (no boost leaks, new brake pads, new fluids, etc.). Check the paint and interior for any flaws and try to fix them. Then get some wheels you like. Then see if you still think your Z is dated. Honestly even with stock rear tails and the USDM front fascia the car looks sleek and sexy.
Note on bodykits.....just don't do it. The JDM bumper may be fine because it's OEM but my experience with bodykits on other cars is that unless it's an OEM part it's gonna suck getting it to fit perfectly.
"The 300ZX Turbo is a dance; it's a song; it's rolling, roaring automotive art. There is no color that doesn't suit it. There is no mood-lifting chemical substance it can't replace." - Automobile Magazine