I believe that renting a scooter does not need to have ANY disability connection. If you want one, you can get one even if you have a briefcase full of documentation that you are in perfect health. It's a mode of transportation, it was meant for those that had trouble getting around and enjoying the parks. If that is because they are fat, believe me they have more then paid for that affliction in many, many ways.
Bottom line...if you want to use a scooter, you can. You don't need a reason other then you want one. When it becomes a problem is when it is used to take advantage of lines or whatever. If I were to rent a scooter, ride to the ride and then get off and stand in line, it totally puzzles me why anyone would think that this was a problem. Can anyone explain how, exactly that would or will affect your visit in any way? Or does everyone just have in insatiable need to feel superior?
I play golf and use a golf cart most of the time. Do I need it? No, I can and do walk it, but, you know what? I find it a lot more fun to drive a cart around. Sometimes people do things just to have fun and enjoy themselves. They pay for it so what's the problem? Many people drive around in a BMW when a Ford Focus will get them there as well. What's the difference?
Waiting ...... As they get to cut ride lines and bus lines. If you need it fine, no problem with that at all. However, if you are using it as a way to get added perks, then no way. A golf cart speeds up play, scooters clog up the parks. Disney does not promote scooter rentals as a way for guests "to have fun and enjoy themselves."