I think you are probably correct in your guess of value.
However the price could go down also, due to unforseen events or circumstances. You never know.
Twenty years ago if someone was to say, well, just point your phone at it and take a picture, then put it on
ebay, most people would have laughed at a strange joke. Take a picture of a stamp with a phone and hang the picture in the Bay? Ho ho.
You see? Hard to say. Collectors will always want to collect I think. It just depends on what is cool and what seems to hold and/or increase in value for the investors to jump on the bandwagon too and drive the prices higher than normal so you could cash in at the time.
A lot of people got hornswoggled ((or hornswoggled themselves) love that word!) in the 70's and 80's and bought everything stamps as they thought everything was going to increase in value.
Years ago people wouldn't have thought China would be in high demand now (unless you were in the know). Personal stamps would sell? Ha!
Sorry, I digress.
Of course it depends on the catalogue valuation of your stamps. $10 or so stamps would be an
ebay item nowadays but who knows in the future? Keep a spreadsheet or database on the market value (what they sell for) of your stamps and watch for a good time to sell I suppose.
I am too busy wanting more and more stamps (accumulator / collector) and studying those I do have to worry about selling or worth beyond a vague idea of common, better, worth a lot in good condition, no matter what the market.