. With the mass produced factory guns its more of (but not entirely in some cases) a parts changing operation. In some cases some wood patches might be needed.
. Cheaper to go find a better Spencer for display and make the junker into a shooter with a modern barrel and a CF breechblock or trade it off so someone else can do the work. This is not the case with Kentuckys (or English or other ML arms). Its just apples and oranges.
I don't think there is a lot of difference, at least relative to the Spencer above. As received, most would have chucked it. Missing or broken parts were scratch built as was the stock. Original Spencers up here are few and far between and many times more expensive than this gun. The same statement could be made for an original muzzle loading long gun. Original kentucky rifles are fairly scarce as well, probably much more so that in the US.
The images below are of the double flint shotgun that I rebuilt (not restored). As found, the odds of it being tossed out were fairly high if the seller had not been an inveterate scrounger and stumbled across it somewhere. I wanted a shootable shotgun and in its present form it not only is one but even if it ends up as a wall hanger someday, it will at least have been preserved and is somewhat unique in the early style of damascus barrels.
What I think is perhaps apples and oranges, is the degree of deterioration that people are referring to. I am referring to guns that are either ready for the scrap pile or not far behind. What others seem to be referring to are guns that might only need a nipple replaced or a broken mainspring and perhaps a cracked stock repaired.
What may also be different up here is that we have extremely few pure collectors and even relatively few who accumulate and shoot original guns. The very few pure collectors that I have met, have all been for cartridge guns and collect only very top of the line originals. I fall closer to the shooter category that the collector category but it is not a very great stretch to say that many of the guns that I acquire to (ultimately) shoot would not in the slightest tempt either the collectors or the shooters that I know.
I probably should also add that my work is far from perfect and I am far less skilled than many of the builders on here. I am using these examples only as guns that have been given a second lease on life until someone more capable than I comes along to take them further.
cheers Doug