Most U.S. cruises especially Caribbean Cruises are focused on islands known for beautiful beaches and water activities.
Having said that most islands also have shopping spots, restaurants, and some guided tours of points of interest.
Since you didn't mention what types of "attractions" you guys are into it's impossible to know what (you) would consider to be worthwhile. Some of the bigger ships are a destination themselves. The Royal Caribbean Oasis class ships offer various attractions onboard (wall climbing, zip-line, Broadway plays, ice skating, water diving show, nightclubs, stand up comedy, casino, specialty restaurants, live music and numerous other forms of entertainment and activities.
If you want to explore large cities and so forth you might opt to fly to Texas and catch a cruise that goes to New Orleans or you might take one on the east coast that goes Miami, the Florida Keys, and possibly Cuba or Puerto Rico. Certainly those destinations would have a variety of attractions.
However it's European and Mediterranean cruises that offer the most bang for the buck regarding site seeing cultural attractions. (Barcelona, France, Rome, Greece ..etc)