This is just a notepad for ideas about how categories should be used in this wikia. It could make up some advice page or section about using categories, or a section in a talk page.
Categories are not keywords.
The fewer categories you have, the more likely those categories will be effective. Looking at some of the pages here (most,actually), clicking on one will bring up hundreds of pages. This is not useful.
It may be useful to have some fixed categories and have authors check on a special page before adding new ones, since use of categories affects all authors. I'm not sure this is possible or even desirable yet, it's just an idea. Whatever, the current categories are not much use and need to be fixed. Limiting the number of categories a page can have might be another solution.
For SEO, and even for searches within this wikia, having a lot of categories make it less likely your page will be found, not more likely. It dilutes the actual text of your page with words that are irrlelvant or only marginally relevant. Some search engines will ignore your page altogether if they decide it is spam. It's best to have between 4 and 15 categories, certainly no more. The fewer you have, the more likely they are to be found, and higher ranked.