You are totally missing the point of a Quad Core Processor.
No one has said it will be fully utilised playing games. The Dual arent so by you method of thought, a dual core is a waste of time aswell.
The purpose of a Quad Core is to multi-task, and they do that exceptionally well. This may include gaming but its by no means limited to it.
Example: I was playing BF2 the other day whilst encoding a DVD. It sailed through where that would be the absolute limit of any top end dual core and probably too much for the low end ones you suggest to even struggle through.
SOme of these E***series CPU's are touching £200 atm. There is no way on this earth that they are better value than a Q6600.
BTW...When you say E4300, thats still about £80 isnt it? I only paid £125 for my Quad. Surely you accept that for £45 extra, that was definitely the better purchase.