So they just happened to have those outfits lying around, just in case someone wanted the fal tor pan???? I think they might just be something that these women wear from time to time.
Since Spock didn't change into a "Vulcan tux" ( or a dress uniform) we can assume that T'Pring is dressed in Vulcan casual. Nice legs on T'Pring, she's the Angelina Jolie of Vulcan. No comment on the "executioner's" exposed flesh? Why would a Vulcan show off his chest like that?