This seems to be something that could very easily be coupled with Mark Trapp's idea for Structured Tag Clean-Up. In addition to identifying bad tags, we can also identify and prioritize good tags that have a bad tag description and tag wiki entry. There are a few questions about tag wikis, such as this one about including books. Of course, tag descriptions/wikis would be cleaned up with the tag (if the tag is actually potentially a good tag with bag questions), and good tags with good questions with poor descriptions and wikis might be a lower priority than getting rid of the bad tags, but I think it's something to talk about.
There is already some generic advice about tags and tag wiki pages on the Stack Overflow blog. I think that refining that guidance to be specific to this group of experts, along with an assessment of the quality of the tag and its questions would be helpful to maintaining a thriving community of people who are able to provide expert advice.
So perhaps kick off a discussion about what should (and should not) go into tag excerpts, descriptions, and wiki pages. Thoughts, comments?