Accuracy depends on a number of things
Firstly, as you very rightly said, quality. This is almost irrelivant nowadays, as all barrels are finished to a high standard. As long as there is a consistent mirror finish on the inside of the barrel, with no scratches or blemishes, then it'll be fine.
Secondly, bore size. Matching the paint size to the bore will no only improve accuracy, but also a minor (a very minor) improvement in efficiency. Barrel kits with a number of bores allow you this option, although many are happy to stick to one bore size (something like a .689, most manufacturers give a .693 with their gats)
Thirdly, paint quality. Accuracy depends most of all on good, round paint. Any inconsistencies in accuracy are usually due to inconsistencies in the shape of your paint
A good barrel (or barrel kit) will most likely be an improvement to a bog standard barrel given on low end markers, but what it's worth to you is up to you. I simply went with a .689 un1tech, and have never had any problems with it