While discussing Rulian Mazan (a unique Purple quality Duty Officer who's a bartender) with a friend, I had a cool idea. Here's my suggestion:
Have special DOffs unlock a new appearance for the assignment givers in your ship's interior. If you get Rulian Mazan, the bartender in your ship's lounge/mess hall now looks like Rulian Mazan. I'm sure the same could be done with other unique DOffs, like Dr. Sibok or Dathan, put them in appropriate places.