What cruise ship is better?

We are planning a summer cruise to western Caribbean on a limited budget for a family of four. We are deciding between the Carnival Valor visiting Grand Cayman, Mahogany Bay(Isla Roatan), Belize and Cozumel and Carnival Dream visiting the same ports except dropping Grand Cayman and adding Costa Maya,Mexico. The Dream is newer and nicer, but it costs $723 more than the Valor. I'm thinking this money could be spent on excursions. We are in our late 40's and have 2 girls 10 and 13 years old. The water slide on the Dream is larger and they would enjoy it more than the smaller version on the Valor. Is it worth an additional $723? I don't really see any more activities on the Dream but I may be wrong. Help!