AMD dual core (socket 939 at least) is going to get cheap, and then most likely disappear.
My take on things is a computer is for doing things, and a dual core A64 positions you to do everything that's going to come around in the next couple of years, including the next version of windows, comfortably; so why not take advantage of a big price cut while parts are still readily available?
If you have any interest in the latest and greatest, bragging rights, etc, then you won't be happy with a cheap X2, period. In that case you shouldn't bother.