DR JohnG, I have Jack Viertel's book, and he signed it for me at last week's sitzprobe. I have not read much of it yet, but I'm enjoying it.
Its approach seems pretty much based on Lehman Engel's wonderful books and the BMI workshop, which Engel began, but unlike a lot of musical theatre books it's tempered by his personal observations from seeing a lot of musicals in their original Broadway runs over the past 50 years. Unlike a lot of theory-but-no-practice musical theatre book authors, he's been in the trenches.