As much as I wish that I had an answer for this, I do not. However, I do have resolution. I started over from the bare image again, and rewrote my scripts from scratch to favor ALSA over PulseAudio - and did not install PulseAudio this time around. Considering the other issues that PulseAudio was giving me, in terms of system stability (or the lack of system stability), I can only imagine that my original issues were also related to that.

On the plus side, I've managed to knock together a decent script that gives me what I was after - volume up/down followed by an indicator tone, volume up/down to exit mute state, and a functional mute toggle through tracking the volume and mute states. More complex than what I was trying originally, which was using pactl to control it all, considering that I am on of the "lucky" ones who cannot get ALSA to unmute.