John,
its power independent. We use both DC and DCC during shows to maximise our flexibility (and the fact that all members don't yet have DCC equipment. If you are careful with crossovers (as in making sure they are isolated properly) you can run both simultaneously. We run DC on the outside loop and DCC on the inside (the inside tends to have more switching opertunities so its better for DCC.
During shows we generally run 2 to 3 trains on a single DC block on the outside and use kill zones in certain modules to ensure that we avoid rear-ending. Of course with DCC this doesn't matter but we generally run no more than 4 trains (of course some people may be playing around on spur tracks while this is happening. I like the DC / DCC mix as there is always action for the public but there is the possibility of some operations on the inside line too (something we're looking at writing some guidelines for).