That's my usual reaction. I've got a drawerful of the worthless things, and probably a little booklet of the newest ones. Years ago, I found out that the post office is not interested in my buying stamps with stamps so I can get the latest: no, they want to stick you with them. Helps them keep the money. And they wonder why people with any choice are using something other than the post office. It leads to embarassing moments in mathematics. It is interesting to guess when the next postage rate will apply: but the practical answer is "it will happen when you have the most stamps of inappropriate denomination."
The real advice? HOLD AS FEW AS HUMANLY POSSIBLE.