August is when many Europeans are on holiday. My wife and I celebrated our 30th with a Grand Mediterranean cruise on the brand new Grand Princess. (by the way, congratulations!)
It was just an extrodinary experience with one not-so-small exception: It was very crowded everywhere we went--and mostly with Europeans. My wife and I are very easy going, low-key people and we have learned to enjoy ourselves in any situation; but given the chance to do it again, I would not go in July or August. My advice would be to go as late as you possibly can--late September or even push it into October if at all possible. It was also quite warm and I think the the weather would be more agreeable in late Sept.-Oct..