saint - I think you are far too personally biased in this to make a rational argument.
I don't think it is fair to suggest that just because someone isn't disabled, they don't know what it is like. My sister is disabled, I have lived with it my whole life. I do know how hard it is.
Disabled parking spaces are for blue badge holders only.
Disabled toilets are public toilets, there for everyone. A disabled person has no more right to them than anyone else. Thankfully, it is now a legal requirement for a public premise to have an accessible toilet. It is not solely there for the use of disabled people.
Disabled people do not necessarily need quicker access to a toilet. Some do, and some perfectly able bodied people do as well. Some people in wheelchairs have bladder issues. Some don't. Some ND people have bladder issues, some don't. The wheelchair thing, is irrelevant.
I would, however, in a queue of say, 10 people, if there were a few standard cubicles and one accessible one, and someone in a wheelchair was waiting, I would let them go ahead of the queue, given that the other 9 people can pee in any cubicle that becomes free, thus reducing their waiting time. The wheelchair user has to wait for the accessible one, therefore they can skip a few places in front. I wouldn't, ever, suggest leaving it constantly empty incase someone in a wheelchair comes along. That is ridiculous.