I don't find them too helpful, so I wouldn't pay full price, but if you are going later in the year, they get down to around $10, I would go for it then.
What I have done instead is sign-up for Groupons and Living Social type things and I think the discounts are as good as the entertainment book. I have them on spam right now because we aren't taking a trip anytime soon, but when I get closer to a trip I will start looking again!