Let me give the arguments why I think we should have this:
- When this website grows, we will need to do add categories eventually anyway. If we do it later, it's going to be a lot more work than doing it now.
- It will be more clear what content belongs to what part of the wiki.
- Lots of pages have a neutral title, but actually talk about WoW-specific topics. This is confusing.
- When people post content without the right category, we'll just talk to them that they should do it correctly in the future. Changing these few pages isn't going to be much, because not that many pages get created. Adding the category issue to the 'wiki guidelines' wiki page will inform people about how it works.

I wouldn't mind to move pages and delete the old referrers if I get the rights to do so.