The text that goes with tags are called tag wiki's. And yes, many on the site do not have any description (and ones that do could surely be improved). The Stackoverflow blog has a post that is helpful when formulating what should go into tag wiki's, and I believe any edits to tag-wiki's need to be approved by moderators at this point (probably only a few individuals on the site have sufficient reputation besides moderators to approve them). So I would say it is hard to imagine negative contribution(s) to the majority of tag-wiki's at this point.
As far as the other problem of tags that have trivial differences, this can be solved with (as mbq already mentioned) tag-synonyms. The general forum policy over time that that has evolved is just to present a thread in meta suggesting tag-synonyms (as only a few have the privileges to conduct such an action).
Tag's are really what makes SO type sites awesome (compared to say email mailing lists). Surprisingly to me, considering the diversity of the people whom ask and answer questions (both in terms of exposure to statistics and differing applied fields), tags have organically grown into meaningful and well defined categories. (Note here I am mainly referring to the creation of tags) While the community (in particular some key individual's) are instrumental to "policing" these tags, it is done so quickly that the interruption of bumping edited questions to the top of the list isn't very noticeable (the same goes for edits).
The only thing to keep in mind (in general) is that this is a community, and so any action that an individual can take that unilaterally affects the community should be discussed with the community before-hand (such as mass re-tagging of questions, see this prior incident on the site for an example of such an action).
Tag-wiki's aren't as noxious though (and need approval from other individuals) so adding a bunch of tag wiki's is probably a good thing (as long as they are thoughtful and reflect how the tag is used in this particular community).
(Mildly unrelated advice) If a particular discussion hasn't come up on the stats meta site, it is frequently good to check out the meta.So. It seems like every imaginable topic of discussion has come up there already.
I realize I didn't answer your question! I don't see much need at this point for a central repository question for tag merges. Those types of pages (e.g. Internet support for stats software) I will speculate are best for content that is relatively static. Tag-synonym suggestions will continually grow with the site in time.