So the forum was down for a bit -- sorry for the delay getting it fixed with all the holidays and such, but I figured I'd mention the issue because it was just weird.
SMF has a Settings.php file (likely so people don't accidentally make the settings readable to anybody), and that file somehow got cut off at 4096 bytes. I'm guessing there was a write failure or something? I restored the rest of the file and things appear to be working, now, but that's a little concerning. I'll likely be moving off this host soon, though, as Hostgator jacked the prices way up. Like 2x what I was originally paying without warning.