I’ve now upgraded to Movable Type 3.2. I regretted upgrading to 3.15 because the anti-spam capabilities were lacking compared to 2.64, but it looks like SixApart has finally recovered the capabilities lost after 2.64.
I’ve managed to bring along my ancillary plugins with just a moderate amount of tweaking. I’ve also changed the file extension to PHP to enable future technological marvels. As a result, I finally got around to writing an old URL forwarder so that references to the old URLs for posts will now forward them to the correct URL for the new layout.