I understand this post is a bit old, but figured it might be able to provide some good info for future travelers. The cruise excursions usually are overpriced and don't offer the best the local ports have to offer.
Most cruises that come close to Tulum either stop in Cozumel or Calico. If you want to explore the best thing to do is catch a ferry to the main land, and then contract some local tours.
Edventure tours offers some good tours and includes Tulum. I specialize on custom tours. Riviera Maya has so many different things to do, that is hard for me to decide what my clients should visit, hence I give them the options and let them decide what works best for them.
Tulum for example is great combined with www.Tankah.com.mx
or with Dos Ojos cenotes.