The biggest weakness with Wikipedia categories, in my opinion, is in how they are used, rather than anything to do with the underlying technical implementation.

Going back to the original example of "American women writers" one is, in my experience, just as likely to find listed a book with a title like "Women Authors of the United States in the 20th Century" as one is to find actual female scriveners.  Wikipedians seem to interpret them not so much as "categories" but "things which might be of interest to people who were interested in this label."

Perhaps if the editors had the ability to say "relatedTopic" in addition to "categoryMember" this behavior could be re-shaped in the future.