We have taken my mother, who uses a rollator or cane, on several Disney cruises (including a few 14 nighters) with very few issues. We only do the classic ships as the Magic and Wonder are the perfect size for her---not too overwhelming in terms of getting around. We do try to stay in mid-ship staterooms and the lower-levels do make it easier to get an empty elevator. However, the key is just to take everything at your own pace. For the muster drill, my parents made their way to their station 15-20 minutes early so they could use the elevators (which I think shut down closer to the official drill time or at least would be crowded). For meals, they either get there a few minutes early or wait and arrive a few minutes late so they aren't standing in the line for very long. The buffets are pretty straightforward and there always seems to be a cast member who offers to carry my mom's tray if she has her cane with her. So, you might chose to carry a cane as it is just a visible cue that you might be moving at a slower pace. Honestly, it hasn't been much of an issue....they do like to get to the shows a bit early to claim a seat at the top of the theater (there is a handicapped section--with regular chairs instead of theater chairs) and my mom uses her rollator then as it means they just take one chair for my dad. If we want to sit with them, we often sit in the back row right in front of them so we are all sort of together. Other times, we just don't worry about it and they sit up in the back and my family finds seats where we want to and just find them at the end.
The only issues she's really ever encountered were when there was a really steep ramp at one embarkation port--this was just tricky with the rollator (and it wasn't Port Canaveral--it was one of the specialty cruises) but not impossible. Also, on excursions--they excursion desk is pretty good about explaining how much walking is necessary--but we've learned to press for details as we've discovered that some excursions (mainly bus tours) will allow her to stay on the bus at some tour sites where the group gets off and goes into a building---so she does miss some elements occasionally, but not much usually (like for example in Barcelona she skipped the walk to Gaudi's Sagrada Familia choosing to hang out in a park near the bus and people watch--but overall she's ok with it. She gets a sense of each port--so it works out. The one thing she as realized she can't do is get off at tender ports as some of the boats are small, very rocky and require several steep steps. She's had hip, knee, and back surgery that makes it hard to balance---so we either pick itineraries that don't tender or she just goes into it knowing she'll enjoy a quieter ship on those days.
