That all depends on your usage patterns
lots of multitasking, having too many apps open slowing things down? then then dual/duaq core will boost you desktop performance.
lots of video editing and processing (not games)? same as above
I would go for it. It will change they way you work with you computer on a day to day basis, You have enough ram to be able to leave apps open even while gaming on a multi core cpu and have no slowdown. But be careful, leaving all those apps open are going to make you want to go dual screen.
for example; I run Wow on 1 screen (windowed but maximized with window no border), and in the other screen, i have web browsers, wowwiki/thottbot, vent, IM, task manager, youtube... etc
closing apps and or alt-tabing is largely a thing of the past with dual cores and dual screens.