There's no way I'd consider camera gear as an "investment." Rarely does it even keep up with inflation. If you want to invest, buy stock in Union Pacific railroad. I use and enjoy old camera gear--I have Petzval lenses from ~1860 & ~1875, two 6x9 folders dating 1914 & 1937, and a couple of rapid rectilinear lenses dating to the 1890s. (I don't own any 35mm stuff.) I consider all of these to be toys in that that they won't give me any $$ return, just fun/entertainment. The way I'm looking at it, the pool of buyers for film gear will always exist, but it will become smaller and smaller, resulting in less & less demand. I've mostly bought camera goodies made before 1900, but even with that I don't see myself making any money on them. The Union Pacific stock will at a minimum keep up with inflation, and probably do better than that. If you want a Leica IIIf then go buy one. Just don't try to justify it by thinking it will be worth more five years from now. Likely, it won't be.
Kent in SD