As for you, #12, you are dead wrong about having to ditch hardware acceleration. Before there was hardware acceleration, game developers tried much harder to eliminate overdraw because it took so long to rasterize 3D scenes without hardware acceleration! The original Quake had zero or near-zero overdraw. If you found a way to make the walls see-through, it wouldn't have bought you anything.
These days, game developers rely on z-buffering and relatively simple culling to solve the occlusion problem, which is really taking the easy way out. Ya, they'll do sectors and portals and stuff, but there's always an amount of "acceptable overdraw" which varies between developers. It ranges from say Quake, which actually tries hard to eliminate overdraw, to EverQuest, which doesn't try at all and just threw everything at the API and the hardware.
Don't get me wrong, zero-overdraw is a very difficult feat to accomplish. Most game developers aren't being TOO lazy about this, and they have enough other stuff to worry about anyway. Zero-overdraw would not help frame rate that much compared to having some overdraw, because z-buffering is very effective. It would solve the see-through drivers cheating problem though.
(I'm not an expert on this but I don't think I'm far off here.)