Library theme sounds good, and I could make an argument for both fateseal and scry being good for that.

In addition, another question to settle, what's the plane like outside the Worlddream? What's it look like, and how does the dual nature change the world? My thoughts are that it's a temperate location where most people live, with the further you get from the center of society the more wild and hostile it is, along with the less seperation between awake and dreaming. Maybe there's a large artifact/temple/ritual site/something holding the dream apart from reality, and the second set is when it gets damaged? One neat flavor thing I'd take from either Changeling (the nWoD game) or the Amber books is the idea of individuals doing risky plunges into the deeper parts of the dream to find useful swag and bringing it back, with the change that the stuff they bring back might not be artifacts, it could be people or even concepts.