A local bike co-op has had a Santana like that hanging in their window for years. People want ready to go tandems they can buy on a whim, and more and more want to ride with their kids, not their spouses or significant others. I'm sure Co-Motion hit on a goldmine when they introduced the Periscope with it offering such flexible sizing options for the Stoker compartment. All the couples we ride with are getting out of tandeming for one reason or another, some after many years, some after just a few. Some Captains will continue with their kids as Stoker but most will not. Some will try to sell their tandems but most wont. Even when they cost thousands new, and all were bought new. Often custom. Me and mine are committed to the tandem concept because she is a blind Stoker. We belong to one of the larger tandem clubs (over 50 teams) and still we are the only team with a blind Stoker. My spouse has had three ex's buy tandems that saw a few rides and then were never touched again. The cheapest of them was many, many, many times the price of your Motiv. It's hard for you to understand just how little wide appeal tandems have out in the world but I'm not surprised that so many of them languish on Craigslist or in co-op windows. The Univega looks 'rode hard and put away wet'. Put away for a long time at that. You've been down that road already. Is there a good reason to wanting to do it again?

At 6'5" you have to know you are on the outside of 'off the shelf' bike sizing. Back in the day any old Peugot or Schwinn could be bought at the local shop with a 27" frame but those days are long gone. So even single bikes must be hard to find in your size. Personally I would say forget trying to find, or even thinking about the prospect of (another) tandem for you and the young ones. That ship has sailed, well, lets say its under way. By your own admission. The best thing you could do for them is get them excellent singles in their size and go out as a gaggle on weekends. If you and the Mrs. want to get that Santana sorted out you would be getting one at a steal of a price. It sounds perfect for the both of you. You could always continue pulling the Mountain Trains with it for as long as that continues to be fun. That must be quite a sight. I doubt you'd be much faster on a tandem with the Mrs. pulling two kidbacks than with the two of you on a tandem and the kids on their own singles. But once every now and then (or more often than that) you two should try to get in rides with just the two of you. FWIW.