Okay, I'm back, with tales of success.
Basically, the only problem was (indeed) your Kobo email and your Adobe email must be the same. Altogether now: "Lame!" I'm not sure who should receive blame here for this silly restriction, Kobo or Adobe. Anyway, I made a fresh Adobe account with my Kobo email, and then the Account settings page showed the device was registered -- after going through a factory reset and re-registering the software (both Kobo and ADE) and the device (KT with ADE). I had to return the book back to the library and re-borrow and redownload it, but anyway, that's not Kobo's fault. Accursed DRM.
So off I go to enjoy some great reads on my brand new Kobo Touch!