going from the standard M4 trigger to a nice gisselle or timney, or another good match/2stage trigger is going to do more for you then a differnt upper/lower
a straight barrel is a straight barrel, your asking if its good enough... well what do you think is lacking? are you missing targets? is the gun jamming? what SPECIFIC aspect of performance are you not happy with?
only thing I added to my Norq was MOE grip, which is 100% better then the standard one IMO,
still shoot it with irons too, no accuracy issues out to 300m... range ends there, so not sure past that... damn restricted...
keep in mind, 99% of accuracy issues are shooter related, so pre emptively buying parts to improve performance is usually not the best way to go about it...
spend money on ammo and training if you dont have an experienced shooter to take you under their wing
someone who is a good shot, is a good shot with any gun they pick up...
Ive seen guys at the range curse their 3000+ ar15s or ar10s because they couldnt get them to hit where they wanted...
and no amount of talking convinces them to listen, stop breathing, time between beats, maintain trigger discipline ect ect...
usually I have to shoot some good groups with their rifle before they break through the ego barrier and start making changes...
heck when I was starting out I SWORE i didnt have a flinch... my damn gun just shot low and left, I swore... despite what some more experienced people told me....held me back for a while... trained it out, now Im a better shooter for it