I have to teach myself everything I know about cars, but it seems that vacuum advance would retard the timing under acceleration. When you floor it, the engine is still not spinning very quickly, so it would have a tendancy to detonate. Also, manifold vac drops significantly, so if the ignition is advanced as vacuum increases, then it would retard as vac decreases. Also, that is why carbs have an accel pump - to keep the engine fed with fuel until it regains enough vac to draw from jets. So, not having the vac advance hooked up shouldn't make the engine fall on its face unless it were to advance so quickly that engine began detonating badly. And finally, vac advance is like a precurser to electronically controlled ignition and knock sensors. If your spark is advanced enough to give you any kind of bad knock, manifold vac would drop, retarding the timing.

Plz tell me if any of my thinking is wrong.