The comparison to the collector car market ignores completely how that market has changed. Circa 1979, a restored model A Ford convert was nipping at $50,000. Just a little heads up, but, someone who bought and paid that much for that car then has absolutely no hope of ever seeing that money come from that car again. They sell for about 12-15K in todays market.
What happened? Tastes, and times ,changed.
Yes, there will always be expensive and valuable old guns, but, as to what they will be, that is a different matter entirely. I doubt Colt Walkers will ever go down in value, but, that is a gun that doesn't see the light of day, much less use, to the average buyer.
A decent old double is a different animal.
I own but one gun that I feel can't see use with modern ammunition, and I don't have a fortune in it. I won't invest in any more guns that aren't usable with steel shot. My belief is that it wouldn't be prudent to my financial situation, and, I am not a collector of anything, save old girlfriends, and thats over too, since I got married.
There are quite a few guys here who buy guns they don't use. That isn't me, but, whatever. If that brings them joy, then what it is worth after the laws and the times change likely won't matter, to them. And, so be it.
I am NOT primarily a clay shooter, I am primarily a hunter. Knowing and preparing for what the future will hold, as a hunter, is no different to me then knowing the daily bag limits, the hours of legal shooting, and where to find the species that I pursue. I will use modern designs, with the shot that is available, and will learn how those combinations are best used to take the birds I hunt. There will be people that sit in their gunrooms, cigar smoke mixing with the smell of the scotch they have poured, lamenting over the new laws, and how it made their good guns obsolete.
But, I won't be there. I'll be hunting.
The future will hold different ammunition requirements. I am preparing for that. The DNR of my state has made absolutely no secret of it. Not a single gun that is/was ever in my possesion was ever too valuable or historic to be put to good use. Hence, putting money into buying or repairing the double of yesterday is all over at my house. Most of the serious 20 gauge people I know have put up stores of bismuth that fill good sized areas of their homes or shops with pallet loads of it, but, that is only going to hold off the future for so long.
In the future, you will use a 12 gauge gun to shoot clay pigeons or hunt birds. You will use steel, since the elements of the earth's crust that are near the atomic weight of lead are far, far more rare, and too expensive or strategic to use as shot. You will have learned that the 12 is just OK for use with steel to hunt birds, and the smaller gauges are just about useless when loaded with steel, save for very small birds, like dove or woodcock. On that note, woodcock will not likely be a legal gamebird in the future for different reasons, but, I digress.
If you are a hunter, I'd advise you prepare for it.
Best,
Ted