It's working. Already. The cross-pollenation of ideas between 4mmscaleagonies and Protocrastinator is already hapenning after only a few short weeks of the two being up. Planning ideas do seem to pass between the two. I have even considered having both layouts exactly the same size and shape with the same trackplan.
I've always believed that "Its not what you've got it's what you do with it" and the idea of producing two vastly different layouts with the same trackplan does certainly appeal. We'll have to see where that particular "train of thought" (sorry about the pun) takes me.