Since I kinda like my stock headunit I was wondering if I HAVE to get rid of it in order to get better sound quality, or would some aftermarket speakers and an amp do it? Honestly I would have serious issues about not being able to use my steering wheel radio controls anymore, and I'm not so sure they can be used with an aftermarket headunit.

EDIT: I have the Rockford Fosgate "package," but from what I understand the only thing that's RF is the sub in the back, is that right? Is that worth keeping?

You do not have to replace the head unit to get better sound, just replacing your speakers will help. Don't get me wrong, a aftermarket head unit makes a huge difference. There are ways to use your steering wheel controls with aftermarket stereos. A couple of people on the board (do a search) have figured it out and some stereos are made to be compatible. As far as what is Rockford Fosgate and what is not, your amps and I believe your headunit is fosgate. It is all lower quality stuff than what they sell as aftermarket, but still good shit. I am not sure about your interior cabin speakers though. Nissan has always used Clarion and Bose.

I also agree. New Speakers will make a large difference. If you are after a major improvement, it is best to replace both. As said above, the RF stuff you have is not as good as any thing that is available in the aftermarket.

What are you looking for as far as speakers? If you buy halfway decent speakers, you will probably have too/want too run a different amp for your in cabin speakers. How much money do you want to spend and how much better do you want your system to sound???