OK, so I did the zergRush method from post 2 (how did I miss that earlier?!) and downgraded. (Double-checked and yes, it is software version 2.2.) Then I ran unrevoked 3.32. I had the same "Waiting for reboot" issue, but this time when I turned USB debugging back on, I got to "Running root..." (instead of "Waiting for system to settle..."). So far so good. But then I got "Error: failed to get root. Is your firmware too new?" But of course, it isn't! I'm back on 2.2! What now?
(And that's radio baseband version 2.15.00.07.28, if it makes a difference.)