After ignoring many, many new WordPress versions, dreading upgrade complications, I finally bit the bullet and upgraded to the very-much-different WordPress 2.6. This mostly went smoothly due to the use of the WordPress Automatic Upgrade plugin.
Unfortunately, I did encounter one major hiccup, the details of which and solution(s) to are described here. Note that while the post only describes a fix to post category name problems, someone gives analogous directions for fixing link categories as well in the comments.
If you observe or experience any problems with the site post-upgrade, please let me know in the comments of this post, or by email. Thanks!
Apparently somewhere along the line, WordPress added tags. I’ve basically been using Categories as tags all this time, when what I really wanted was tags. Maybe I’ll write some SQL stuff to go through and convert categories to tags at some point.