Low vacuum - should I ditch my vacuum advance distributor?

[2] If that is an aftermarket dist you have, it should have an Allen Key [ 3/32"] inside the nipple. Screw in fully CW, softest spring setting. This is usually about 5-7" of vacuum, & it should pull the VA actuator in because as it advances the timing, the vacuum increases.

You can adjust that vacuum advance for lower vacuum to activate the advance also.
^^^Easiest, most effective $0 solutions.