Thanks for all the replies, I especially enjoyed MikeandJean's post - inspirational!
In answer to some of the questions. I have an Avid single digit 7 with travel assist on the rear and Paul Mini Moto on the front (I replaced the other Avid SD7 in the hope of getting better braking power. In my opinion, not much difference). The pads, Kool Stop MTB, are pretty new and I usually readjust every couple of rides. I replaced DT Swiss hubs a couple of years back with Phil Woods hubs and at that time had the Arai drum brake re-installed. I understand that it can be tricky to get the mounting just right and there might have been some braking loss as a result. I inquired with Co-Motion years ago about retrofitting the bike with disk brakes and it was a significant amount of money ($3K?). Here in Santa Cruz there are several custom builders so it might be possible to have someone weld on a disk brake mount.
I planned to offer the travel cases and frame covers as part of the sale. Thanks for the suggestions of eBay, TandemClassifieds.com and Bikeflights.
We're looking at buying a Calfee Adventure Tandem, inspired by AKExpress' posts, and would like the ability to do gravel as well as road.
Thanks again, I'm leaning towards selling and if that doesn't work out keeping it. BTW we also have a Cannondale MTB tandem.
ps - I would disclose to prospective buyers my perceived deficiencies of rim brakes