I have heard of people buying these forever stamps in huge quantities, as a hedge against inflation. Even if you don’t need to use them, you should be able to sell them for 5-10% less than first-class postage in the future.
Of course, the USPS could at some point say: “Forever expires next week.” and kill the value of your stamps...
Since the middle of the 1970s postage rates have been pretty well matching inflation.
I was considering buying another couple books, but I realized I still have almost a full book of 2008 Christmas stamps along with two and a half books of forever stamps. At my current rate of usage (all bills except taxes are paid through the web) I already have enough stamps for the next couple of years except for Christmas cards which I always get that year's Christmas stamps. If I start hoarding the glue will dry out on my Forever stamps before I use them.
Precious metals are a much better hedge against inflation than mass-market postage stamps.