I've been tracking these threads (re: Thunderbolt display won't wake up, and similar) for a couple months, desperately trying all of the suggested solutions. Intermittently my display would shut off and then not come back on without disconnecting the power and reconnecting.
Meanwhile, seemingly unrelated, we were having an occasional flickering of our lights, sometimes almost like a "brown out," where the lights would dim and flicker for 10-15 seconds. Well, the power company came out and found a lose connection in our transformer box (near the street). My Thunderbolt display has been working flawlessly ever since.
Theory: There's protective circuitry in the Thunderbolt power supply that, when it detects irregular line voltage, trips off. This is to protect the display, but requires a disconnect/reconnect of power to reset. The voltage drops in my house were causing the display to "protect itself."
So, if you are having this trouble with your Thunderbolt AND you've noticed the lights in your house flickering occasionally, you might want to have your power company or an electrician investigate. In our case, no other electronics or appliances had trouble with this; only the Thunderbolt.
In our case it was a problem at the transformer. Line voltage drops can also be caused by lose connections in your breaker box, a breaker going bad, a short in your house wiring or even a lose lightbulb arcing in its socket. Some of these situations can be very dangerous, so perhaps your Thunderbolt is telling you something important??