I'd guess that most Mind Flayers WOULD value physical beauty in female slaves, much in the same sense a human farmer might display some pride in a prize heifer. Not that this attitude would do the female in question any good, of course!
I'll throw in a random plot idea... how about a group of mind flayers running a game of Survivor in a human village or small town. If a 'thid is discovered by someone and not mistaken for a human (there will be ways to verify this), that one is "thrown off the island". Of course some of them haven't the slightest idea of how to "act human", and will make a variety of missteps that may or may not be ignored by the populace as "normal strangeness". Let the plot advance a little bit, then add the PC's. Or maybe the PC's ARE some of those mind flayers!