I love Golarion. I think it is a pretty fantastic setting. However, this has brought one of my obsessions to life.
I also really love stats. There are quite a few threads (most of them in the Pathfinder General Discussion board) on demographics and what is appropriate and not appropriate. And while they are frequently interesting and very good at getting the creative juices flowing, they're all based on the posters individual settings, which while they are sometimes called Golarion, they are not actually Golarion.
I would love a book that breaks down the demographics of the Inner Sea region by things like class, race (and maybe culture), level, and stats. While there are a few books that give a general outline of what things should be, there's not really any hard details at large, just occasionally for individual towns/cities. And even then it's not broken down by all four of the aforementioned subjects.
I think that would be an extremely interesting and useful book to have, and I know that it would certainly help me better envision what kind of characters I want to play and how they would influence/impact the world.