I stumbled on this book in the Menlo Park public library and really enjoyed it. I also wondered why I had never heard of PLATO. Very good read.
Xerox PARC researchers visited PLATO in 1972 and when they got back to Palo Alto they implemented just about everything they saw! App generator for pictures (SD Mode), paint (charset editor), bitmap /memory graphics display (plasma panel), multiple fonts and character sets, etc!