I went back to the Trinket. It's putting out static only. Same sensor, same amp. So, maybe I cooked the Trinket. I'll have to decide whether I want to solder up another Trinket and perhaps sacrifice it this year or wait until next. As for now, I've spent a WHOLE LOT OF TIME working on something that already worked, I have the bigger cauldron, and I have a switch, and it works again.
My other upgrade for next year is to put the Trinket--or Uno if I can't get the Trinket to work--into low-power mode while it's dormant to save battery and avoid having to turn it on and off so much. I've just learned how to do that in concept and this appears to be a good application.
So. I can take it to work tomorrow to entertain my co-workers. Since Halloween is a Saturday, I'll decide then if I want to spend more time (and maybe money) getting the Trinket version to work again.
I feel much better! On to 3.0!