Wow... you mom sounds like she was pretty dedicated @happyme! I'd keep saving the newer stamps you get in the mail since they have actually become much scarcer now that so few people use stamps to send mail. Whether they become worth anything remains to be seen... but if you decided to get rid of them, at least they would still make a nice contribution to a local Boy Scout troop-- as I recall, they still can earn merit badges for stamp collecting.

Stamps are very similar to comic books, as far as collectibles go. My ex was a comic book collector, and some of her "near mint" Silver Age books we're quite valuable, but most were just printed paper. In stamps, 99% will never be worth more than a penny... even if they are old. It's that 1% that makes things interesting.