There's no sense in choosing socket in expectance of longterm "upgradability".
Only people that will ever work for are OC hobbyists that goes through a number CPUs in a rather short time. And then only because it saves them the hassle of changing MB. Even so it seems OCers goes through a fair amount of MBs too, so...
I'm sure AMD haven't changed any plans of substance.
DDR3 isn't in sight, because there's not enough market drive yet behind it. For that reason it's necessary to go DDR2. Why? Because it's a solution for larger amounts of ram. We're moving towards 2, soon 4GB ram.
The important thing about M2 is that it will be minimal inconvenience for MB manufacturers. It's still basically a 939 board.
You also need to understand that lots of pins result in an expensive package. A significant part of the retail cost of a CPU.
Multicores is an exciting development, but early on you'll get good benefits from dualcore. There doesn't seem to me to be terribly much sense in
rushing quadcore, or something else, until software have been through a transformation.
The thing is, Intel has to be gently led onwards towards new strategic mistakes

, the dual, large Conroe cores. AMD's best hope for surviving a few years more, is that Intel continues to counter/follow the last thing AMD did. The upcoming Conroe is basically an Athlon64 X2 on steroids. It was expected. There's not much AMD can do to directly counter that. Intel have vastly superior resources and is also able to get better paid for their CPUs than AMD. AMD's only hope lies in not revealing it's hand, whatever that is, too early.
Finally, considering the capability of your current system, I can't see why you're so agitated? You should be able to relax and sit comfortly awaiting whatever materializes in the future. And if quadcores, or something else, is late in coming at consumer prices, I can see nothing wrong with dual core. Should be viable for a good while.