Thought about it... what's wrong?
Quad Core performance wouldn't improve unless the application or game is multi-core enabled. It's not worth the cost of upgrade, since 3.21Ghz Duo Core is already a good speed.
i7 Core started off as a quad core redesigned with two threads per core, with one main feature in mind reducing bottlenecks in the system processor to make it work faster by being smarter technology.
Tri-memory DDR3 slots on a motherboard (rather than the standard duo slots) work together in 3 ways rather than 2, also reducing bottlenecks because of this re-design. DDR3 is also faster than standard DDR2.
I'm not saying it's needed and you would also probably have to upgrade the motherboard to support it. Rather costly!
In the end I think the current processor is fine to use, you can still play the latest games at a high resolution.