The difference is that the AUMF is qualified by the words "necessary and appropriate" which does not imply an unlimited power. The AUMF was also aimed directly at those responsible for the 9/11 attacks, it wasn't some open ended declaration against terrorists in general. The WW2 declarations by contrast, pledged "all of the resources", not merely those "necessary and appropriate" to go after a specific group. That's the difference. If Bush wants a delcaration of war on AQ in general and wants all the resources at his disposal, why won't he ask for it?
I can't think of anything more necessary and appropriate to this war than intercepting a phone call between al Qaeda and the US. To me, it's not a close call. It's a slam dunk.
If you're going to tie the President's hands like that, then you're basically saying that the President doesn't have war powers at all.