Reports from Berkeley and NYC suggest there is a sort of a "critical mass" of rationality communities, above which they quickly become really really awesome.

The awesome effects include, for example: enough clout to start projects that change something important in the world; and developing a communication culture that supports improving your thinking and knowledge of rationality much faster and easier than in single player mode.

So I imagine a rationality base mostly puts enough people together to reach this point.

Also, I'd personally be in just for the fun of having a secret base :)