We went on a 3 day for our first cruise just to see how it would go (I get motion sickness). We added on days at Disney so while we had more vacation to do besides the cruise, I thought the 3 days was a nice getaway. There were several people who said they do this particular 3 day cruise every year (the Friday after Thanksgiving) because it allows them a quick cruise without really having to take off much work/school. If it fits nicely into your schedule it could be a great getaway as long as you go into it knowing you can't do everything. Pick the one or two things everyone is most excited about and and then just relax.
The benefits to the cruise is you don't have to plan anything like you would if you went somewhere else - accommodations, restaurants, entertainment is all done - plus paid for! It can be a stress free vacation. If we were going to one of the other places you mentioned, I would want to research fun places to eat and would definitely have some must-see attractions that would make it a more "active" vacation vs a "relaxing" vacation. I would sort of look at it the same way I view a Disney parks vacation vs a
Disney cruise. One we go-go-go (and love it!) the other we relax and soak up the sun (which we also love!) So I would just sell him on the peace and tranquility!! ;-)