"I want to say, in all seriousness, that a great deal of harm is being done in the modern world by belief in the virtuousness of work, and that the road to happiness and prosperity lies in an organized diminution of work."

Bertrand Russell - "In Praise of Idleness" - http://www.zpub.com/notes/idle.html

"Leisure: The Basis Of Culture" by Josef Pieper also seems on topic, I'm planning to read it myself - http://www.goodreads.com/book/show/767958.Leisure

References are from comments on here yesterday - "How did we get so busy?" - https://news.ycombinator.com/item?id=7769610

I don't know if the OP is still contracting but if he is, something like Brennan Dunn's "Double Your Freelancing Rate" could help with working less on more interesting / higher paid projects - http://doubleyourfreelancingrate.com