I did some more research and my symptoms and the code pointed to a bad EGR valve. As it so happens I found an online coupon for advance auto that was $40 off for every $100 spent and they had the EGR valve in stock for $110, so I got it for $70. That was hard to beat, because the next best price I could find was $84 at rockauto.com (plus shipping).

If anyone else is interested in this deal, the coupon code is CCABIN, it's about a 1/4 down this page...

So, I bought the EGR valve online, drove to the nearest AA that had it in stock, picked it up, went home, installed it and reset the CEL light. I immediately noticed a slightly smoother idle (I mean smoother than the already fairly smooth normal idle). No hint of the idle stumble on the way to work this AM either, so I'm pretty confident it was the EGR valve afterall. If anything changes, I'll update this thread.