Two books:

How Equal Temperament Ruined Harmony (And Why You Should Care) by Ross Duffin.
Duffin mostly advocates bringing the thirds a little less out of tune, as they are so far out of tune in 12TET. That would mean something like quarter comma meantone. He does say the best tuning depends on the song.

Actually this article here compares Duffin and Isacoff's books and I mainly agree with it.
http://www.artsjournal.com/postclassic/2007/01/the_tuning_tide_turns.html

Evening in the Palace of Reason by James R. Gaines.
Sort of biography of JS Bach and Frederick the Great. Bach kept making tons of music because of his faith in god. He actually wasn't all that popular at the time. The galant style was more popular, which seems to mean lighthearted, fluffy, etc. Bach was darker, and more profound. And his counterpoint, lots of stuff happening at the same time, instead of a single melody line. People supposedly found that too serious. So the author says. Bach was just about forgotten until long after his death. Some of his greatest works were barely played even once until decades and even up to a century later.

It is hard to imagine putting the effort into writing all that music, knowing it might only get played a single time. Or that you'll send the sheet music to Frederick The Great (some of your best work ever) who's just going to throw it aside and never listen to it even once. It would seem to take something like faith in a god, and a belief that your music was written for the glory of god, to bother continuing to compose so much. To work so hard at it. If not that exactly, something else about as mystical.