Something that I've wanted since MOO is backgrounds to the interface showing city scenes.
They could just be some pre-rendered scenes, on a loop like a DVD menu. Just something to give the impression that the player is in the universe instead of just a screen jockey. You know, like what was going on in the background of Corosceant (Jedi forgive my spelling!!!) in the new Star Wars films.
They'd be subtle, blurred maybe (shallow depth of field), behind the interface.
Now, I'd put some elbow greese into 'em. Have some rain roll in and out. Maybe have a sunset scene; all the variants could be randomized.
There could even be some variants of rioting if approval sunk too low -- smoke rising from buildings in the distance, periodic explosions now and then. If the world was under attack, a variant could show some bombardment coming through the city. Then, of course, there'd be a turn or two with cranes and the like to repair the buildings!
Like the title says, it's all purely cosmetic. I just have always thought it'd be a nice polished touch, especially to go with such an outstanding game.