..it's commonly held that cruising without vac advance usually is inefficient with poor cylinder filling and insufficient advance for complete burning.
..who have disconnected their vac advance and indicated a richer a/f reading?

The purpose of vacuum advance is to advance the timing under higher vacuum low load conditions. Advancing the timing will always lean out the mixture. So if you disconnect the vacuum advance the AF will get a little richer. I've done this many times on the dyno and in car.