Spock occasionally called Uhura "Miss Uhura." As for why Spock was called "Mister Spock," Amanda stated in "Journey to Babel" and Spock also stated in "This Side of Paradise" that humans are not generally capable of pronouncing the Vulcan family name. It's a compromise so other people don't have to struggle to pronounce a long surname that likely doesn't have many (or any) vowels.
As for names and ranks, what's with everybody except Janeway being on first-name basis in Voyager? Janeway calls everybody by their first name, no matter if they're on duty or not. And Harry Kim, addressing Tuvok as just "Tuvok" without either "Mister" or his rank...?