New post (second update) to liven-up this thread.
Found a clue in this ongoing mystery.
After resume from suspend and with the screen irrecoverably black:
if the system is then hibernated (typically by closing the lid), then upon resume from hibernate, the backlight is switched back on. (!)
This is reproducible (works 100% of the time), and is the first workaround -- if one can call it that -- to return usability of the computer without a reboot. (Still too much trouble, though. FGLRX driver is a far better solution.)
So if someone can figure out what is happening in the boot sequence (on resume from hibernate) to turn the display on, then a good workaround to this problem should be a snap. ( ?? )
Clearly, whatever command is doing the trick is not getting sent during a resume after suspend. Or maybe it's sent but blocked. Or...
Found this after totally borking the system and being forced to do a reinstall. (Caused by a repair after install of a crazy Brother printer driver, and even after 17 hours of attempted rescue -- to no avail.)
Any of you gurus have an idea what the magic command is?