I'd echo John's statements above. Two worlds... those of shooters and those of collectors. I think with plain rifles of lesser value, the bore condition may play a bigger role simply because there are fewer attributes to value the gun by and bore condition is one of them. But as the artistic and historic value of a gun increases and it becomes more of a collectable than a shooter, the bore condition becomes less and less of an issue. Of course, there are always exceptions, and some shooters probably shoot great guns that should be more protected as collectables... and some beginning collectors acquire plainer rifles where bore condition is one of the few factors available to base value on.
We all prefer decent bores in our guns, but as a long-time collector of American longrifles, I'd never pass up a good rifle simply because the bore was rough or heavily worn... and other than looking at the muzzle for any unsightly damage and for traces of rifling [always like to know a gun's bore size and rifling pattern], I pay little attention to what's on down in the bore... other than if it's loaded or empty! In a way, heavily worn bores add character to rifles, showing they were really used and played a role in America's development... and were not just closet queens.
So as John said, if you shoot, be careful with the bore, but if you collect, look at the entire gun and don't let a poor bore deter your decision to buy.
The one caveat to all this is collecting target rifles. They are a different breed, not made for hunting or protection, but specifically for precise target shooting. Target rifles, in my opinion, should have fine bores, otherwise their value is significantly dimished.
Shelby Gallien