It is just portraits and music. Think of it as DLC. I had promised to keep the game open source, so no gameplay-relevant stuff could be made paid-for, so a cosmetic DLC made the most sense. We're working on adding Events, like in Crusader Kings or Stellaris, and some of that content might be Enhanced Edition only, depending on how things look when we've done more work on it.
Glad to hear you're enjoying it