So we are looking at two different situations here; the use of titles and the use of names (or nicknames).
With titles, I think it's pretty easy. Dr., Senator, Miss/Mr./Mrs., it's hard to go wrong there. In your example of the pediatrician, I think since your relationship with her is strictly (I'm assuming here, I know) based on her capacity as a physician, I would have called her Dr., but I don't think it was a huge faux pas that you didn't, as she didn't address you as Mrs. Princess. I know my doctor socially, so when I see her professionally she is "Dr." but otherwise she is "Julie." But that's a different scenario.
With politicians, calling them by their title is showing respect for the office, if not the person. I would have to have true disdain for one to refer to them as Ms/Mr (as in Mr. Obama versus President Obama).
Your priestess friend was absolutely correct, I think. They wish to be called by their chosen title within their religion, but don't want to extend the same courtesy? Absolutely not. And their refusal to compromise with first or Mr Last Name would be a conversation ender. Their obvious complete lack of respect for the beliefs of others is appalling. I am not Catholic, but I still call the priests I know "father" because I respect them, even though I don't share their beliefs.
Your aunt sounds a little kooky, but if she wants to be called "smells like a skunk," there's no harm in it. If not doing so is going to upset her then why not just make her happy. It harms no one and pleases her, so where's the harm.
Finally, as for formality...yes, if someone is going to insist they be called "Mr. Jones" then I would prefer to be called Mrs. Hami. There is nothing wrong with either position; it again boils down to being called what one wants to be called. There's nothing retaliatory or rude about being called Mrs. if that is your choice, for whatever reason.
The only time I can recal being unwilling to call someone what they wanted was when I was a newlywed. My ILs would have liked for me to call them Mom & Dad, and I just cannot do this. I have parents. But they were cool about it and we just went with first names. Funny, though, toward the end of his life I found myself referring to FIL as Dad sometimes. But that was after 20 years of knowing him. So I guess if it is a title that hasn't been earned, I wouldn't call someone by it, but otherwise I think it's okay.