I get this site doesn't like talking politics but it has been a largely Republican lead effort to 'starve the beast' and this is a simple fact easily confirmed by looking at voting records.
Most recently: https://www.congress.gov/bill/116th-congress/house-bill/2382...
But it wouldn't ever lose value and could inject some cash into the USPS.
There are some issues with postage stamps as an investment, though. They're not as liquid as T-bills, though if they become a popular investment that problem solves itself. More worrying is that the USPS is not quite as reliable a borrower as the US federal government - can you really be certain this would never lose value? I'd like to see where the bond ratings agencies would rate USPS stamps.