It seems I've mostly solved my blog woes. I got some quite helpful replies (still visible on Blogger, although the comments didn't come over to my new blog). I also got emails from Will Guaraldi about PyBlosxom, and from Lloyd Dalton about blog_my.
I took at least a brief look at each system mentioned in the comments and emails, but I decided on PyBlosxom. If you're reading this in a web browser, what you're seeing is PyBlosxom rendering a theme I ported from Tumblr, with all of my old Blogger blog's content imported. Quite frankensteinian indeed, as far as blogs go.
It turns out that my impression of PyBlosxom's size when I wrote my "blog woes" post was a bit off – I didn't realize just how little functionality resides in the core. It's pretty slim, but with a decent selection of plugins. I only needed tags, wbgarchives, and metadate, but there are plenty more for those who want more features. With the tag and metadate plugins, I managed to keep my blog posts in almost exactly the format I've always used, so that was nice.
PyBlosxom nicely solves my biggest concern, which I didn't explicitly state in my original post: I want to keep all of the files related to my blog in a Mercurial repository. I've succeeded in that – my entire blog is in Mercurial now. That includes configuration files, the .htaccess file, the template, the entries, and even the queue of unfinished entries. If I ever need to, I should be able to move the blog to another host in a matter of minutes. Not that I ever intend to leave WebFaction (note: that's an affiliate link), which is where it's happily hosted now.
With that all out of the way, hopefully I can quit the detestable practice of metablogging, which I'd managed to avoid for my entire first year. Thanks to everyone who made a suggestion, and special thanks to the PyBlosxom developers.