But you won't have the amp that comes with it... Sadly, it's only a 50W unit mounted on the inside of the firewall under the dash.
I would say, it might be a slight upgrade over what you are starting with, but on a scale of 1 to 10, yours starting at a 2, the R/F system as installed by Nissan is maybe a 3 or 4, at best.
Mainly, the sub is very muddy and doesn't hit very well. Understanding that you probably aren't playing rock concerts from your truck regularly, but trust me, coming from that to better aftermarket components, it's night and day.
Secondly, the door speakers are junk. Even with a better amp, they still aren't much better and probably won't survive the extra wattage.
If you want decent sound, I'd recommend you save a bit and go with better quality aftermarket items. You can do it a bit at a time... HU, sub and amp... then door speakers... maybe add some tweets... You don't have to do it all at once. Plan out the system and add to it over time if you have to. You will be much happier with it in the end.