Let me start off by saying I'm 27 years old. I have gone from buying guns to collecting, looking for quality not quantity, having a very specific focus on S&W's and Winchesters. With that comes the added interest in the accessories, holsters, grips, boxes etc. I am "unique" compared to my peers because I have a keen interest in history and social studies...I appreciate the historical factor of firearms but also the craftsmanship. I've learned in a short period of time that you need to be very focused if you're buying for investment purposes... and LUCK is involved. There is a reason why Triple Locks, "357 Magnums", 27's, early 29's command higher prices and will continue to in the future. Same for Winchesters. But as the time moves on I can tell you need to adapt your strategies if you're investing.
I think we have seen a peak in prices for antique firearms on a BROAD scale. My generation will understand the value/price and "cool factor" of a Colt SAA or Winchester 1873, but up to a certain price. We are too far removed in age and history. That will affect the broad market. The exception comes down to condition, rarity, and configuration. I still see 95%+ condition antique guns making new price highs in the future, even if demand weakens, so will supply. I only buy .44/.45 caliber and .30 WCF Winchesters. It's what people want, and the ammo is still available or being made. We have seen the resurgence in .45 Colt, .45-70, and even .44-40. I have shifted my Winchester focus to the smokeless era and collect the 1900-1945 time period for that reason. If you shoot the gun or can shoot the gun it will help its value. I don't buy...25-20, 32-20, 38-55, 40-82, 45-75, etc for that reason.
Back to Smith & Wesson's the same rules apply, but if for investment sake buy the highest quality and most rare examples you can find and time will tell. I still see a strong 20-30 year run ahead. But as prices go up, the market narrows and that problem will continue. My generation buys plastic because they're cheap and they have student debt. But the millions of new shooters will recognize quality as they age and eventually have the resources to buy the collectibles.
If you want to speculate on what will go up in price...then buy what you like and enjoy owning it. I see a strong future market for Performance Center guns, particularly pre-lock Stainless guns from the 1990s. There were lots of special order configurations and limited quantities for various models. But others tend to agree and prices have sky-rocketed on those guns in literally 3-5 years. I have a few guns that have appreciated 100-300% in that time... it's luck.
A lesson I've learned in investing within the financial markets is you make your profit when you buy not when you sell. My collection began as buying the affordable stuff at a deal, and I covered every small auction I could to find the guns and deals! You have to put in the time if you want the reward. I have now reached the point, where I'm having to "pay up" for quality and the rare stuff. A novice collector gets to the point where you need to decide if you have the stomach and wallet to be a serious "collector"...I'm at that point. It's hard to find a deal on Pre-27s and Triple Locks. That is why many here enjoy simply owning these great firearms, shooting them, and enjoying them! I have guns I won't fire because of their condition, and sometimes that sucks. So I often focus on 95-98% condition guns that I can shoot a couple times a year and still be collectible. So decide what you like, what you can afford, be patient and buy the good guns at a good price if you can. Remember prices don't change overnight... this is a gradual change over decades and don't waste your time worrying about losing or gaining 10-20% on a gun.