I may be the minority (and no flaming here), but if I return to the same resort I already have a mug for, I bring my old one with me.
If you went to a fast-food place that offers free refills, would it be OK to go back to that same place, say, one year later, walk in and refill the same cup from the previous visit because you paid for it back then?
Because that's what you are saying. If you purchase a refillable cup, mug, boot, sock someplace, it is OK to return to that place later and continue to refill.
Prices rise on drinks because of people like you. If you can't afford to buy a new $12 mug on each visit, maybe Disney is not the place you should be vacationing.