SOLVED:
In one of those, "I'll only figure it out after I publicly declare my incompetence" moments, I figured it out.
I thought perhaps that even though I wasn't seeing any burn marks on the circuit board, that maybe there was some sort of a blown connection. So I tried hooking power up to the other two ends of the switch, and in the process, noticed that the copper connector from the diverging track's hot rail was jiggling loose. I pulled it up, and sure enough, it wasn't attached and appeared to be oxidized on the underside. Rather than mess around with it, I just decided to jump it (see picture). And voila, we're back in business.
So chalk that up as a new one for RealTrax switches that I haven't seen documented on the site before: oxidation on and loosening of copper connectors. Relatively easy fix as long as you don't mind a dab of solder.
Thanks all!
Rafi