I didn't know that they were allowed to sell stamps anywhere for over the actual cost. I don't use many stamps anymore, either.
For packages, I've had much better service with UPS than USPS. The post office tracking is horrible, and it is much slower. I can send a package from home (NY) or FL, where I winter, to our grandchildren in PA vis UPS and it will be there in 2 days. Sent via USPS, it's 4, sometimes 5.
As far as media, I think as soon as you send a book that has a card with it (as a gift, for example), you can no longer send it media mail. You'd be better off sending it them separately, with a note in the card that the gift is arriving in a different envelope.