It has been my experience that the vacuum goes away SO fast the timing returns to whatever it was at that rpm. If it is to low at that rpm when I "nail the throttle" I do get a slight hesitation. Advancing the base timing a little more makes the hesitation go away. Therefore, I must conclude in my case the vacuum advance add's little to address the hesitation problem. Don suggested, and I concur, that instead of running so much BASE advance, which causes starter problems, that I increase the advance curve of the weights and springs. Go for more advance at a lower rpm by changing springs and a more aggressive curve as the rpm builds. BUT, if you end up using springs that are too light, the weights don't return properly everytime, so the timing tends to bounce around at lower rpm. In that case, you would lighten up the weights themselves.
I'd like to run 22 base and a 14 bushing with a more aggressive curve and a max in at 24-2500 rpm. I will probably need a timing retard electronic to get the starter to agree to that. The starter is "she who must be obeyed" you see.
Why do I run vacuum advance?
Two reasons:
1. More advance at light throttle under cruise rpm conditions will generally optimize mpg. Which in turn increases your total range in miles before having to stop for gas.
2. My engine HAS to idle about 900-1000 rpm. When I finish adjusting the carb for best idle rpm, the throttle plates are open enough to cause "run on" or "dieseling" when the motor is hot and shut down. With vacuum advance (ported to DIRECT intake manifold vacuum) I can get my 1,000 rpm idle speed without having to open the carb plates as much. So the motor dies smoothly when shut down because the throttle plates close more completely and disallow that little bit of extra air/fuel to be drawn and cause the "run on" condition, when hot.