Shane,
I have insulated both rails between the main lines because that is a requirement of Ntrak modules, which many sections of my layout were originally planned to be.
It is my understanding that it is better to not use common rail wiring practices on DCC equiped layouts. I do have the layout wired for DCC, but double insulated tracks are not necessary for it. In fact, it would probably be better to not have the tracks insulated at all. However, I will have a way to connect all the tracks electrically--probably by feeder wires that will be routed through toggle switches of some sort. (I don't have all that figured out yet.)
Presently, the track is powered through rail joiners and widely spaced feeders wired from buses which run under the layout. The spacing between the feeder wires will be reduced as I get the time, which will also reduce the need to depend upon the rail joiners for a good connection. Hope that helps your understanding of my wiring.
Here's a picture taken at Union, Oregon, on the layout