When I was cleaning out my house to sell, I found folders of stamps my father had bought and held onto with the thought they would grow in value. But, when I took them to a store that bought old coins etc, they told me that the younger generations don't use stamps so don't appreciate them for collecting.People buy stamps to collect and NEVER use them. Again that eliminates a low cost source of revenue.
Per Google unless stamps are from before 1930 they only have face value. I wound up putting them in the donation box, though if I'd realized I would move to this retirement community where people are so far behind the times that we still have to mail checks to our clubs, I would have kept some of the old stamps and used them now! ha