WoW is GPU limited, but I still see a framerate boost from setting processor affinity. I run 2 wow's on a laptop, and setting one window to use cpu0 and the other to use cpu1 boosts my framerate. This does not contradict your "WoW is NOT CPU limited" statement, but helps ensure that the cpus work optimally. This helps somewhat with what you describe under #4. Zoning times will still be slow due to the lonely harddrive working overtime.

Many are suggesting quad-core solutions. Initially I thought this might be a good idea, to keep framerates ok even with 4 visible wow's on one screen. But I don't really know how quad-core processors work. I'm guessing the architecture (and the way the OS uses the cpu) is the same as a dual-core? If indeed so it would perform pretty much as a dual-core system. But memory and GPU would already suffer too much with 4 windows onscreen for it to work well.

One interesting area is SLI cards and gfx card drivers. I'm on thin ice here but if you got 1 card to render the top part of the screen and the other to render the lower part...

I havent tested much, but when I get home I'll test with multiple wows on my main computer, which happens to have a 7950GX2 SLI card.