i recently got my hands on 350z tanabe gf210 springs and koni shocks got them for a great deal, slapped them on and drives as good as it looks.(on 03 sedan)
also put oem staggered 19's very happy with the outcome and cost me less then a grand for both mods
but if you dont wana worry about problems stock isn't bad at all, recently had to cam shaft position sensor issue, cost a grip for maintence just to keep in mind

 

I got some used 18" coupe rims a few years back and they look sick on my car. I also powder coated them black since my sedan is black. The 18" sit flush with out any need for spacers. I'm not going to drop the back since the gap is minimal but I need to lower the front a bit. Send me a PM for a few pics of the rims if you're interested

 

what are the signs of the cam shaft position sensor issue??

 

If I was you I would start with the recalls FIRST. Yes there are recall issues. The dealership will replace the recalled parts at no cost to you.

Second since you also have an 03 I would replace the stock radio and climate control panel as it will quite on you as it has for the rest of us 03 to 04 owners. Granted you can wait on these things but what good is it if you have a pimp ride with no sound or air?

Lastly I recommend you check these too: the third brake light, parasitic electrical drain, and lack of a dipstick for transmission.

I have had mine for a few years now but I find myself looking for another car, maybe BMW next................

 

Yes. Upgrades are nice, and I would advise you to get some.