If you drop .tide files in ~/Library/H9 Control/Presets/<algorithm>, H9 Control will properly read them on launch, but for some reason it only imports .h9z or .syx files. This seems like the simplest case of "I had this .tide file synced to dropbox and need to import it on some random machine in a hurry". Since that's the way H9 Control stores the presets on disk, why can't I just import those files instead of doing a bunch of Terminal mucking?

Well, we could support this but no one has ever asked for this before.  For the most part people use the export features in H9 Control to get their presets, and that exports h9z files. One reason why we use the h9z format instead of just importing and exporting tide files is that our plugins also use .tide files, and there are some H9 algorithms that are also plugins, but they aren't using compatible preset formats.  In any case I'll add your request to our wish list.