Is this Demon just junk or am I just junk at dealing with it?

The vacuum at idle is useful to track.
9" around 800-900 is fine. That's about what I figured. I ran a CC H280 for a long time. The MP probably has more seat to seat, so comaprable idle characteristics. As you clean up the idle it will probably improve.
But idle speed and vacuum in neutral can be misleading. An engine can be run very lean when all it has to do is overcome friction. The real test of power is in gear.

As far as the power valve, if its not leaking and the gaskets not split or something, leave it alone. Later, much later, you can test for opening point.
The squirrters are irrelevent. Later, much much later, pump shot can be looked at. It's there to cover for delay when quickly opening the throttle when the carb is supplying most of the fuel from the 'idle circuits'. 'Idle circuits' supply fuel any time the air speed past the boosters is relatively slow. That includes low to highway speed cruising. Hardly any power is needed to keep a car moving until interstate speeds.

You might find it useful to look at Chrysler Master Tech sessions 222 (1966) and 273 (1970)
Master Technician Service Conference - Chrysler's Training for Mechanics