Hmm I was thinking you could add rotating cubes in the 3D skybox, with less of a stroke on the outside and actual lighting, that would spin as Penguin says, and as someone else said they could spin faster and faster the more control points were captured. Also, they could be rotated themselves to make it seem more random. Maybe even make them float?
Also, on a more random note, if this map ever has sequels, YOU MUST PUT IN ALL MANNER OF THINGS TO KILL PEOPLE RANDOMLY. Such as random pits that open up into the floor, random vents that catapult things into the air, random spikes to skewer people walking above them. All of these could be marked by individual decals too :O
EDIT: I can't find it right now, but if anyone has ever played that hilarious game where the aim is to kill yourself ass many times as you can in two minutes, and deaths by some ways (get in a rocket ship and hit the ceiling for example) are worth more than others (spike pit)