Two different thoughts here for two different issues. I have run manifold vacuum for advance on a handful of vehicles. I've done this for optimal around town and highway cruise fuel economy (lots of advance at and just off idle is great for trail riding fuel economy). With any performance driving manifold vacuum drops off quickly as the throttle is opened. This can work well for heavier load applications as well, open teh throttle a lot to get a heavier vehicle/load moving and your vacuum advance drops sharply off, once up to speed and off the throttle vacuum advance comes back in for an increase in fuel economy.
Put a vacuum gauge in the car, ideally two vacuum gauges, one to manifold one to ported. Watch how they react in comparison to the other. Also get an adjustable vacuum advance can as you will want to limit how quickly vacuum advance comes in depending on the engine/vehicle/and which vacuum source you use. One thing though, regardless of which vacuum source I use I will always get my machanical curve set how I want it first. Vacuum advance is not a band aid, it is simply "extra" timing to help with fuel economy if the application will tolerate extra timing at part throttle or cruise.