It will help, WoW likes CPU speed more than anything. People who say that it isn't an intensive game on ultra are clearly not moving past vanilla areas though.
Back on my old rig, let's see, it was:
E8400 Core2Duo @ 3.0ghz
4GB DDR2 Ram
8800 GTX. I had some really icky framerate problems. Like 20 FPS in Dalaran and 25 man raids. This was also at 720p, my PC was super well maintained too. I could've cut down my settings more, I guess, but I didn't really want to! I ran most things at notch below, except for the basics that you really want to look perfect. 2xAA, 4X AF.
That was 2009, around Ulduar, and the specs went up again with Cataclysm too with the new effects and another large asset boost up. Their engine doesn't really resemble their vanilla one at all, it can just run it's assets, so don't look it as a 2004 release.
My new one is:
I5 750 @ 4.0ghz
4GB DDR3 Ram
460 GTX. It's mostly all good now, dips to 50 at full ultra (w/ high shadows) in super intensive spots, like the main drag in Dalaran, but I'm not complaining.
I wish I had an SSD though. And man am I glad Dalaran is basically gone except 70-80 leveling. Fuck you, Dalaran.