Milspec is a minimum standard, but not always what someone needs. A chrome barrel will put up with lots of auto fire and 5,000 rounds a year - but chrome isn't as accurate, and Uncle Sam only has a 2MOA standard on it. A plain barrel will do for a lot of casual shooters, and one properly nitrided will be worth the extra cost, too.
There are lots of trigger jobs are there, but any polishing will still reduce the case hardened surface on the sear engagement. A better option would be to install the trigger adjustment screw modification. My AGP lower came with one, and it takes most of the creep out of the travel. I lost about 75% of the wasted motion - which also eliminated 75% of the grittiness in the travel. I don't have to pull thru it. The travel adjustment is limited by the trigger tail bearing up against the safety. It can be ground for clearance, for now I'm living with having enough movement to make sure the safety functions correctly. No sense making it "unsafe."
Carefully consider if an adjustable stock is really needed for a couple reasons. Do you have an extreme length of pull problem - such as when wearing body armor and shooting in a squared up position? Is living with the harsher action of the carbine extension worth it being shorter? Carbine buffers are known to be too light, or even contribute to bolt bounce. If shorter isn't mandatory, consider the A1 stock with rifle buffer setup, as it gives a comfortable and consistent cheek weld, and is stronger. Most of the "marksman" and long range AR's use a fixed stock as it promotes more accuracy from the shooter.
Don't forget the current issue M4 is a bundle of compromises to satisfy different uses by different soldiers. You don't have to accept the negatives that come with it, you can specify what you want and have it fit what you do.
