A few ideas for Gallifrey.

For starters, I think that the Cloisters under the Citadel should have a bit more content, like Weeping Angels, as well as Matrix Ports, where the Matrix could be accessed from. Secondly, I believe the addition of the Cloister Wraiths would also be pretty cool, with basically Time Lord textures, but made of stone and with the screaming face. Also, the Cloisters should have the actual Cloister Bells, basically bells but with a few changes to their game mechanics. Finally, perhaps, littered about the landscape of Gallifrey, there could be new structures, such as crashed Saucers, Time Lord gunships, and small town structures, possibly with some destroyed building. Adding on to that, the addition of Gallifreyan mobs would be a nice feature, as having Time Lords and guards as the only mobs is dull.