I completely agree! The ship is easy....everything is laid out beautifully to accomodate wheelchairs and other aids.
But the excursions are another thing altogether. I don't know where you will be stopping, but most of the port we went to, you would have to stay on the main road. I don't think they are required to follow the same laws when building in the caribbean. In Grand Caymen, there were stairs into most of the shops and no ramps, making it very difficult to get anywhere. Costa maya went okay since almost everything was in a flat area. Cozumel was okay with about half of things accessible.
Good luck and have a great time!