As for stamps, I used to collect stamps so I know what happened to that market. The "bible" for stamp values, Scotts, decided that since everyone automatically discounted their "book price" by 20% to get actual value, they simply reduced all of their book prices by 20% so that their book would be correct. The market continued to take their book price and discount it by 20%!! In the end, it was better to mail your unused stamps than to sell them. I remember using stamps issued throughout the 70's and 80's as postage for almost a year.
I think that vinyl market will die with the last generation who grown up with records. Like stamps or baseball cards it depends mainly on nostalgic feelings for a disappeared world, (like my youth I presume ). A Michelangelo's drawing is a unique example in the history of mankind, but a Jutta Hipp's record is simply one of the many ways to reproduce her art (the music).
If you want something similar to a Picasso's sketch, in term of investment you should buy the original master at least.