Something I wanted to try was repainting the chrome spoiler. It detaches fairly easily and you can do a black with clearcoat, or even order some Graphite Shadow (Nissan code KAD) paint and try doing it body color. I have a GS car also so I'd love to see that. That would probably cost you about $40 for paint, clearcoat, and primer.

One cheap mod ($25) I did was to buy two white 12V LEDs (dimmed) and wired in some ambient lighting on the driver and passenger footwells. Looks kinda nice and gives the car a nicer feel when driving at night. Might as well replace the license plate light (if you prefer white). Also, converting the turn signals to LED would be kinda cool also.

 

There are tons of topics on mods. It just depends on where you want to start.