Does this resolve the crippling Daggerfall bug where all quest objects (items, enemies, etc.) were invisible? Given the mindbogglingly complex dungeon sprawls in that game, hunting for invisible items was somewhere between nightmarish and... something worse than nightmarish.

I have spent lots and lots of hours with Daggerfall, from the beginning, but never encountered the bug you mention. This isn't going to help you, I know, but it says at least that it's not a general problem, but may have to do with your PC or with your installation.
That said, I know that Daggerfall, at least in the beginning, had many bugs, most of which have been patched over time.
Are you sure that your game version is 2.13?

I owned Daggerfall back in the day, and it worked fine; this was a bug when I tried running it five or ten years ago on windows XP, I think. I had heard it was fixed in an unofficial patch, but wasn't sure if it was real or if this included it. Sounds like it does, though.

I believe that bug was caused if you had your # of files set too low in config.sys (One of the start-up files in DOS)

Assuming gog uses Dosbox for Daggerfall, it's easy to fix