Considering the writer's background, I was hoping that Allende's Chile would be sort of the end-all be-all for books on Pinochet, Chile and the coup. After finishing, I'd say that it's not even close. But the story is still worth looking at.
What this book truly is, is just what it says: an inside view. There are significant passages on America's involvement, Pinochet and Chilean society at the time, but Boorstein really concentrates on political and economic conditions five to ten years prior to the coup under the the Allende government.
Some of the economic details get excruciatingly boring, but some of the historical background and personal experiences are what make Allende's Chile worthwhile.
For a more detailed look at American involvement, I'd look to someone like Christopher Hitchens and his book on Henry Kissnger.