OK, I managed to get things going again, but in a totally ad hoc fashion. As others have said here and elsewhere, this is no way to roll out a firmware update across 4 different hardware versions of a critical piece of kit! I was caught in an update loop: updated firmware which wouldn't accept my just-saved settings and also wouldn't allow a downgrade. What to do? Taking advice from a different thread I:
1. removed AC power for at least a minute
2. while that counted down, I pressed the hardware reset for about 30secs (who knows if that mattered?)
3. unplugged all cabling, including internet from my cable modem, leaving my computer's ethernet in port 1 (an old requirement on old hardware)
4. applied AC power again. This always allowed me to access the 655 as admin, but nothing removed firmware 1.34NA. Apparently its permanent, at least until the next update(?). But I could not restore my most recent settings file (or any other settings file for that matter). Downgrading was not permitted (I came from 1.21) really leaving me in the lurch about what to do next. I was left with a basic default routing table that at least allowed me access to the internet.
Then, after reading others' experiences, and without being sure what did what, I did an additional factory restore from the admin page, and began yet another attempt at loading settings. My browser (Safari) spun its wheels for awhile, and after say 4 minutes(?) I manually stopped the browser-loading and was faced with the login page. The only difference was, this one didn't accept the usual default of no password. And when I typed in my password, hitting the Enter key did NOT work (as it always had in the past). Only when I mouse-clicked the OK button was I (finally) able to confirm that I had indeed restored my router settings with the new firmware on an A3-version of the 655. But upon replugging my modem into the WAN port, I still couldn't connect to the internet. The last hurdle (for me anyway) was to reboot the modem (perhaps releasing the ip would've worked too?).
At last, after an hour and change of troubleshooting, I was back to where I started. Its been about 14 hours and no glitches or surprises yet. But left with a bad taste in my mouth.
Hope this helps somebody...and thanks to all who contributed their experiences. It definitely kept me from giving up. D-Link, do your homework and be sure these updates work in the usual fashion and not by a technique out of the distant past!