what an interesting thread!
and for me, old habits die hard as I address any officer as sir or ma'am...including my commander-in-chief and any former commander-in-chief. I would probably be inclined to salute if I were in uniform but that's just an instinct, lol. But that courtesy extends on down to civilians with no rank or title, also.
Yeah, I would err on the conservative side and address any former President as "Mr. President" in person.