Yes, you are right. The short term value definitely drops. Anyone who buys firearms as a short term investment is more than likely to lose their shirt.
In the long term, however, as models change, values can go up. I have a S&W model 66 which has a counterbored cylinder & pinned barrel. It is worth more now than when it was originally purchased in 1978 (not by me). Or think about pre-reminginton marlins, or pre-64 Winchesters. No one thought they were buying a collectors item at the time, just a gun.
Not being contentious at all. Your point about the classifieds is right on the money and will hopefully help set people's expectations. If you bought during the panic, your best bet is to hold those firearms and maintain them until either another panic or they appreciate over time.
From Belloq in Raiders of the lost Ark: "Look at this. It's worthless - ten dollars from a vendor in the street. But I take it, I bury it in the sand for a thousand years, it becomes priceless".