Sounds like you were already wanting to spend more money...

More ram and an ssd will make a huge difference. I bought a newer video card and it didnt make much difference. I dont know anything about intel cpus but i have a four core amd and ram + ssd + 64bit os made a gigantic difference. It was literally like a new computer. I was also contemplating just building another computer but now i know that would have been money wasted. And im not even overclocking the cpu. Wow is heavily dependent on cpu and ram, at least according to some blue posts.

If your cpu is old then i guess new cpu, ram, and mobo would be the way to go. Id try one of those two routes before going all out unless thats what you already wanted to do from the beginning.