Wrong. WoW is actually optimized for 3 cores. It consists of a large main thread, large sound thread, and then about 40+ smaller threads (check for yourself using Process Explorer). A quad core is perfect, as it leaves the 4th core open for background processes such as Ventrilo and a browser. Also, if you went from an E8400 to i5 2500K and noticed no difference, you either spend all of your time solo or are lying. In a raid, there would be a world of difference between the two.
In crowded cities and raids, your GPU is not what's powering your framerate. In an MMO there are too many calculations required (player/mob positioning, spell casts, damage done/taken, etc, etc). That's why the CPU is your biggest upgrade. Now, if you're standing alone in Ashenvale, then yeah, a better GPU would yield better framerate. Unfortunately, that's extra framerate when it's not needed, whereas a better CPU grants you better minimum framerate during intense situations, which makes the game more playable.
Once textures are loaded, the SSD grants you exactly zero fps. Good financial investment over a better CPU, which grants those extra fps during the scenarios where the difference between 15 and 30 might be the difference between a dead boss and a wipe.
SSDs are a quality of life improvement. Things load faster. Once those things are loaded, it sits idle and grants you no performance. If you already have a top of the line (or even second tier) CPU, enough RAM, and a strong enough video card, then yes, it's a decent addition to make life easier. It's not, however, the single largest performance boost for WoW.