Before I get into using power banks for this I need to boost the voltage a little, which will help me get more out of the D-cells anyways. The motor I'm using for the dispenser seems to struggle with quick dispensing once the battery voltage drops below 5.3 volts. I made a simple voltage booster with yet another 555 :) and an n-channel MOSFET that I think will keep the vibration dispenser working more reliably until the voltage gets below 4.5 (and the NE555s stop working). This would stretch the lifespan of alkaline batteries a bit and set the stage for me to experiment using a rechargable 5V 2.2A USB power bank instead.
I think this will also provide a little more flexibility on what motor you use, and let you crank up the RPMs a bit more for larger containers where the weight of the peanuts make the dispenser harder to vibrate.
I haven't added feedback with a comparitor yet - will try it out as-is and see what's needed.
Also adding a small shelf to a larger jar so the weight of the peanuts doesn't dampen the vibrations.