The only place you see differences are in raw speed, based on gigahertz power, or multiple processor use, which is rare with current software.
I can type the same speed on a Word document with a Pentium I as on an Intel DualCore. DVD playback is a constant speed, regardless of processor. Net surfing is more dependant on connection than processor. Well, you get the idea.
For Games and Video Editing, as you listed, it can be quite helpful. Whether it's $1000 better depends on what you have now.