I remember back in the 1970's when there was a huge craze over Model 12 Winchesters' Today they still bring less than they did in 1980. OTH, a CVA factory finished squirrel rifle is today worth double or triple what they cost new. Same for some other black powder guns. For instance a CVA flint big bore 58 caliber Mtn Rifle, is now worth double the new price. Trying to guess what will increase in value is like drawing cards one out of thirteen is an Ace. I have been collecting old (1900 ish old) hunting and fishing magazines and catalogs. Not so much for their value, but also for their interesting content. I managed to collect a few things that went up in value enough to call an investment, but most stayed the same or went down. Years ago, whenever I took my kids to McDonalds, they got the first of one kind and then I kept the next unopened Happy meal toys in a box in the attic. They went up and then back down. Depression glass has risen and fallen. Older Game News pre 1980's seems to have been a good deal. At one time National Geographics would bring more than new when they reached a certain age. Now folks cut out the car ads and frame them to sell at the antique car shows. Paper collectibles are not worth as much as they once were because you can scan them and make 400 copies. The most bizarre collectible that paid that I am aware of is porn. I worked for a firm in Miami and an elderly man died. I and a secretary were sent over to inventory the house. and contents. There was a safe. Safe cracker came and opened it. Inside were hundreds of very old porn pictures. I mean like 1870's to 1900. I heard from the partner that the old man's collection of pictures was sold to a European buyer for over a hundred grand.
Old Cuban Mahogany floor model TV cabinets from the 1950's and 1960's can bring over two hundred dollars just for the wood because the hard stuff that once grew in the Caribbean and South florida has been timbered almost to an concern species. The market rises and falls for many things. Ten years ago Sassafras lumber was bringing a several dollars a board foot for export. Not so much now.