There are plenty of upgrades and things you can do to a less expensive AR15 to make it better.   As long as it’s a Mil-Spec gun, go ahead and replace the springs first off, make sure the proper areas are staked on and don’t get carried away.  Staking your gas key is probable one of the biggest things I’ve seen AR15 owners not pay attention too and if you shoot enough rounds, you’ll find out what  happens.   Gun magazines are an obvious area of importance, but many still think that they will get good reliability out of their guns.
I call bullshit on that one and the complacent gun owner is going to be the one that has the firearm go down at the wrong time.   It’s been a few years, but not that long that a guy who had put on a Spikes tactical upper receiver  on his gun stated that he runs his guns dry and doesn’t have problems, well that is another individual that is going to get a shock when his MOA AR15 goes down after rapidly firing off 30rd and that dry run firearms goes down.   Complacency is something that really catches up with a gun owner or Law Enforcement officer.   If you want a better gun, learn how to upgrade it or maintain it properly and just buy a better barrel or upper receiver.