Here's my take on it based on my experience: bore condition matters little generally speaking when you are talking about antique American long rifles since most of the guns have pretty awful bores and are purchased as artifacts and art more than as guns by many collectors. An original, particularly attractive, signed gun with a poor bore is still going to bring good money, but if that same gun had an excellent bore, it would probably bring more but not probably as much more as if it was the type of gun someone might buy and actually shoot. However, alterations such as "stretched" barrels like Rich mentioned certainly impact value.