Like the OP, I've bought hoppers and not used them before, disappointed in the waste; then traveled quite a few visits without them (especially with little kids who can't do a super-long day). Next trip, I think we will consider them for the following uses:
- we like to use crowd calendars and feel like we've had good luck with crowd avoidance that way. However, we've never taken advantage of EMH because of that (those are usually higher crowd numbers) - hoppers would let us spend most of the day in the lower-crowd park and still use the EMH at a different park
- we go in the fall with Halloween party and Food & Wine going on. Those greatly affect the crowd levels in MK and Epcot - hoppers would let us spend partial days in those parks as needed, but get out when crowds are high
- Still regarding fall party season - evening shows/fireworks schedules vary and we may want to spend a day in one park, but still want to catch a night show at MK that we couldn't see on our full MK day. We could hop there just for fireworks
- we are not afternoon break at the resort people. We might "break" by choosing a restaurant in a resort for lunch, then able to hop wherever we'd like for the evening.
- We're interested in trying an Epcot resort - hoppers would definitely allow us to spend lots of partial days there, rather than one loooong, hot day wandering World Showcase
- We may be staying a shorter trip than our usual next time. On an 8 day trip, we have 2 travel days, 2 MK, 2 Epcot, 1 each DHS and AK. On a shorter trip, I'd cut something to 1.5 or .5 and want to mix and match.
- If we were ever able to stay a lot longer than our usual, I'd want hoppers because we may not need another whole day in a particular park, yet still want a few hours there.
- We may be interested in fly-by-the-seat-of-our-pants dining ideas. . . we've always set 1 ADR per day, which attaches us to a given park. We might like to try just looking for ADRs much closer to our travel dates instead of 180 days out and this would leave us flexible to pick dining anywhere we like/can find with a good time instead of limited to certain parks certain days.