Well, I putzed around with it all afternoon...and then, Success!  (With a capital "s", no less.)
I noticed that the lever-cam for the electric choke was jamming. I could poke it loose with my finger, but it would stick again when I rev'd it up.  I removed the electric choke assembly and looked at the cam teeth. They had been worn rough from the end of the high-speed idle screw, and had created a divot in one of the teeth.  I filed this smooth so the teeth wouldn't catch and re-assembled it.
Back to normal.  Not sure why it picked today to fail---and what an odd thing to fail---but I figured it out.  Runs great, now.  
 
And now, the rest of the story...
I took it out for a quick run to "test" it out, nice acceleration down the freeway, back through town and then as I approached the turn to my house I went straight and drove down into a redwood grove.  Partially for the fun of it, and partially to test out my new PIAA driving lights.  Got to a good turn around and decided to take a couple of pictures of driving lights to post here.  When I got back in the car I noticed my tach had dropped to zero and needed to be reset, so I turned my Cobra off...

It wouldn't start---either all of the starting over and over again drained the battery, or my new lights eat more power than my alternator is delivering---and I was deep enough into the grove to get absolutely no cellular reception

.  I pushed my Cobra onto the entrance of a private bridge and luckily for me (I was at least a mile from home) caught a ride up the hill. A ride back with jumper cables and I was on my way.
 
My Cobra is on my trickle charger as I write.
DD