Turns out the Concours didn't need a new bulb, it just needed some more electrical connection cleaning. After replacing the bulb that wasn't blown I finally took off the fairing only to discover that, like all the other electrical gremlins, it was a matter of dirty connectors.
After cleaning up the wiring harness, suddenly all the lights work again. I posted what happened on the COG discussions and got this pearl:
As usually happens in a case like this, you immediately see the good advice repeated. Only a couple of nights later I was reading Performance Bike Magazine. They do a bit each month on what to look for in finding an older model sport bike, in this case the thirteen year old Honda VTR1000 SP2. In the article they suggest that cleaning and protecting all electrical contacts on a bike that old is a good winter-time activity. If it's true for well cared for sports bikes half as old, it's even truer for my field-found Connie.
As WillyP states above, bikes aren't built to keep out the elements, even the most covered bike is virtually naked compared to a car. Even in the case of a well cared for, covered sports bike, cleaning the electrical contacts is a worthwhile off-season ritual. In the case of a field-found Concours, it's where I should have started in the first place. A breakdown and electrical cleaning is my go-to next time around.
As a project bike the Concours continues to teach lessons even as it becomes more and more roadworthy.