We get the refillable mugs each time. Sometimes when we go we way we aren't going to or (heaven forbid!) reuse our mugs from a previous visit. But we always get them anyway. Usually on our first a.m. my DM will go to the food court to get some coffee and return with 3 new mugs. She says it's her treat!
Are they a good value? It all depends.
When we go we always have a rental car so we stop off at WM or Target on the way in and grab some food for breakfast (in the room), bottled waters, and (until recently) a 12 pk. of Diet Coke. So why do we get the mugs? Hmmm...my DM enjoys a cup of coffee in the morning and I like my Diet Coke. Since we don't usually buy breakfast in the a.m. the mugs are great to get our morning drinks in. And on the occasion when we do eat breakfast in the food court we get 2 bottled beverages to drink later. When we drive to the parks we take our cups, with our morning beverages in them, and drink them on the way to the parks. Then when we return to our resort later in the day we stop off at the food court on the way to our room for a refill.
Sometimes, when it's really hot and I plan ahead, I will take our softsided cooler and fill it with ice and bottled waters and Diet cokes. Then when we get back to our car we will use our refillable mugs for a ice cold drink on the ride back to our resort. Really nice after crossing the scorching hot pavement, especially at AK where we always seem to be leaving the park during the hottest part of the day (AK usually closes at 5 while we are there).
Last year for the first time we used QSDP so we got the mugs anyway. This year we will again so we don't have to decide to buy or not.
Could we save money by not buying the mugs (when we don't get them free)-Yes.
Did I like them better when each resort had their own design? Yes.
Do I have a nice supply of mugs already? Yes
Will I still buy one when we don't get it free-most likely, Yes.
For us, it's also an inexpensive souvenir. There have been trips when it's the only souvenir we buy. We are not big souvenir buyers. And I enjoy using the cups when watching DD11's softball games at night-with hot tea!