Well, after (cough) a few months, I’ve finally updated MT-Notifier with the updated version the author sent me, oh, back in September. Rrg. (And, yes, I’ve updated that version to the even latest version.)
Anyway, the good news is that notifications on a per-post basis can now be subscribed to.
The bad news is that, well, I managed to lose old notifications in the process (my fault, not the upgrade fault), so anything you were previously subscribed to, you’re now not. Sorry about that. Though, since Notify hasn’t been working here for a few months anyway, I assume it hasn’t been a terrible hardship.