Many, if not most of us, have the same problem. Since I sell duplicates on three different forums, I am slowly using mine up. Still, on THIS forum, for instance, I could not sell a nice selection of MNH 22c commems for 20% under face, so that tells you something.
You can sell them on
ebay or bidStart and probably get 80% of face (for a larger lot), then put the money into something you find more interesting, another hobby, pay off debt, etc. Paying off credit card debt gives you a huge return on investment, as it stops those 18% to 24% interest payments every month; that's like free money in your pocket.
There's also the possibility of finding a church or organization that makes monthly mailings, and offer them not only a discount, but also offer to apply the stamps yourself (so they don't have to find volunteers to do it), and that will use up a large amount in a short time. As postal rates go up, the demand for low denominations of sheets goes down and down, since there's a physical limit as to how many you can stick on an envelope. The packages I've sent since Christmas have had as many as FIFTY 5-cent stamps on them, plus a few higher denominations. It has taken me two years to "train" the postal clerks at my post office, but they now accept my stamp-covered packages as the "new normal" and cancel them very nicely, as well as accepting my count without question. Good luck with a common problem for U.S. collectors.