Update since my OP last Feb...
I was able to find a Yuba Mundo to test ride and it was a good fit, a pleasant surprise since I'm 6'6", all legs, and bikes usually aren't designed for people like me. The other cargo bikes under consideration either didn't fit or couldn't find one to test ride (didn't think it ethical to feign interest just to get one in inventory).
So with my options narrowed down for me, started watching the used marked. Followed for about 18 months. Two things of note: 1) These really don't hit the used market very often - in the Monterey Bay/SF Bay/Central Valley area there would typically be 0-2 Yuba Mundos for sell at any time which were either electrified (Bionx Hub motor) or had the more limited gearing (7-speed vs. 21-speed) that would be problematic around our somewhat hilly town. 2) Cargo bikes seem hold their value quite well, never did find a great steal.
Time spent watching the used market gave me more time to use my road bike+trailer combo. As my kids grew and gained weight (crazy how fast they grow!) I really started noticing it more on rides. And as they graduated from preschool to elementary, the school commute got longer, with a few more small hills. I do a lot of biking so still doable, but a slog. Eventually concluded that an e-assist was the most practical option, especially after leg day or boot camp workout.
We ended up getting a Yuba elMundo (their electric version). Glad we waited because they have moved from the Bionx Hub to the mid drive eRad. I love the mid drive. It's very well integrated, seamless and non-intrusive. It senses pedaling, braking and shifting which means the motor only kicks on when you actually want it. The motor can take advantage of the gearing, lower gears for climbing and higher gears for the flats.
With the e-assist our school commute actually takes a little less time as compared to the car! We bypass part of the bad traffic areas by using bike trails, and we zip past the traffic at/around the school. The ride physically, even fully loaded, has the feel of a nice walk rather than a grueling leg workout.
The entire setup was not cheap, but going by the AAA cost per mile estimates, if we do even half the trips to school by bike (and I think this is a conservative estimate) then the bike will pay for itself in about 2 years. There are lots of misc. trips around town that I will use the bike for, so it will probably take even less time to pay for itself.