I read this thread and looks interesting. I support ChannelingGinny's theory ...
QUOTE
Who's to say that dementors don't "kiss" muggles? This could perhaps explain psyche patients, and perhaps even trauma patients, that go into a vegetative-state. Maybe the dementors took the opportunity to suck their souls and left an empty shell of a human? Muggles don't know about dementors and therefore would have no explanation why people are comatose. Yes, a severe brain injury will do that, but I'm talking about people who haven't had head trauma (or other severe bodily injury). You hear about cases where a patient "just slipped into a coma" for no apparent reason, since their other symptoms seemed to be non-threatening.
Could it be that you think wizards exists? Because I do!

And I'm always trying to explain thing that can't be explained with science, or have a complicated way, by the existence of magic.
Anyway, Dementors
do affect Muggles as well as wizards; the only thing they can't do it seeing them. And agree with you in that of Dudley was in the wrong place, in the wrong time, and that's why Dementors tried to kiss him. Wizards and Muggles' souls means a delicious meal for them with no differences. I think they don't have preferences at time's meal
Do you suppose that Dudley's encounter with the Dementors finally convinced him that magic was real and that his parents were full of misconceptions? Do you think this affected Dudley's relationship with his parents...especially his father?I think it could be. We can picture that when saying Harry goodbye, that he kind of 'rebels' against his father (ok, not literary, but he delays the departure only to inquire about Harry). Maybe it didn't change his mind the following week, maybe not even the following month, or maybe yes, but a thing is certain: he had to have changed in some way. I don't think he could have fully accepted magic or wizards; perhaps his change was only concerning to Harry.
I'm still wondering what was so terrible to make him change, though. If somebody could answer that ... I'll give you a prize