For now, though, I decided to explore vibration isolation options without solving the problem of having a too-heavy camera on this motor/prop combo. The two materials I tried in v-1.0, felt and closed-cell foam tape, both failed to damp whatever frequency of mechanical vibration was causing the camera to be shaky. So, I went for a known solution of memory foam (e.g. McMaster PN 86195K314).
There's a 1/4-20 screw going into the bottom of the camera that, with a large washer, sandwiches the camera mount in between two pieces of memory foam. Here's what it looks like on the frame:
The improvement in video clarity was impressive, though it didn't eliminate the vibration completely. The camera is still too heavy, so the whole thing is hard to fly and the motors and ESCs get hot. But here's the result: