any suggestion?

 

lots of people get the roof spoiler off ebay from a seller named Shadowspeed something. they're awesome they come paint-matched and look great. Stillen also makes a roof spoiler, little pricier needs to be painted but also looks great.

for the spoiler itself you can either get a Nissan OEM one from courtesyparts.com or from ebay as well, lots of people have added a spoiler to their car and there are write-ups on this site of how to do it as well

 

I have the Ebay roof spoiler ($80 shipped). It isn't a dramatic visual because it is not as large as the more expensive versions, but it's ok from the side and rear.

The trunk spoiler...I bought mine painted from the dealer and they installed it. The kicker is that the Nissan OEM spoiler includes the LED 3rd brake light which has to be wired in to replace the rear window brakelight, if your car is so equipped.

If you buy a trunk spoiler off Ebay and have it painted, you may not have that light. I'm not sure if it is DOT legal, but if the existing internal light still works, I'm not sure.