I'd like to suggest an approach for handling material that differs between the show and the book (or that is expanded upon in the book). The best approach I have seen comes from the Game of Thrones wiki, which uses the TV show as its chief point of reference. Then, where appropriate, it adds material from the books, in a section in each article generally called "In the books." (Here's an example.)
I think this is a smart way of doing things, and I think we should follow it here. Most folks who visit this wiki will do so out of interest in the show, so that's our obvious focal point. But where it's helpful, we should include information from the book. As an example, I've preliminarily done so on the page for The Grasshopper Lies Heavy.
On a related matter, there's one issue we face that Game of Thrones of course does not: actual history. I think there are certain pages where it would be valuable to explain what happened "in our timeline," so that folks reading can have a better graps of how the TMITHC universe differs from our own. Again, as a preliminary example, I have done this on the page for Adolf Hitler. If this approach is deemed valuable, there are some other pages where we'd want to include information like this, such as Reinhard Heydrich, the Kempetai, etc.
I'd be very interested to hear any feedback!