Thanks very much for all that input. In the morning I'll rip that 'ol EGR valve off and give it a good inspection and cleaning and see how that does. I'm sure water got into it when I had that little "incident" and I had overlooked it until you said something.
My first guess on this whole issue was a vacuum leak so I went back and made sure all the manifold bolts were good and tight and then did a leak test using a propane torch.
I took the car out for a good twenty minute spin around town just now and noticed that the problem seems to be intensified as the engine gets to full operating temperature, though advancing the timing did help a lot (kept it from dying at every red light!).
I'll post my findings in the morning... Thanks again for the input.