Thanks, Larry. I think I get it.
First, because I'm working in SP NAD83 Feet, I need to convert the MaxPS to meters, then apply the equation. So, for MaxPS 270, that converts to about 80 meters. Plug that into the equation, and I should see the image at scales higher than about 300,000. When the MaxPS is 1, that's about 0.3 meters, so I don't see the image until I zoom in to about 1:1,100 meters. The extent of all four tiles in my study area is just over 1:7,000. So, when I increase the MaxPS up to 6, that's 1.8 meters and computes to a scale of 1: 6,800, and so the image appears.
Now my question is, why don't I have overviews generated for the master mosaic dataset? Even after building overviews, there are no additional footprints and attribute records in the footprint layer. Overviews were created for the three component mosaic datasets, so why not for the master mosaic dataset, which is a mosaic of all three? And why would creating the master mosaic compute such a small MaxPS for the 2009 mosaic in the first place?