Back in the late 1800's this topic was discussed at length and it still goes on. A gunmaker of the time stated that only the last inch of rifleing is important, and to prove his point he made a spiral rifled barrel...that is the whole barrel was bent around a mandrel so it looked like a big corkscrew. The last inch was left straight, and the rifle shot as well as any of the era. It was a high velocity air rifle, but the principal holds.
I own several c.f. handguns, and one of them has a fair bit of pitting in the first 3/4's of the barrel. It is the most accurate of all I own for some reason. I'm certainly not saying the rough bore will improve anything, but at least in this case it sure hasn't hurt.
Pitted bores will lead faster shooting cast, but a few rounds of jacketed bullets clean them up nicely.