How much is a good amount of money to use on a carnival cruise?

Ragin’ Asian asked:

My wife and I are talking about taking a cruise from miami. We were going to arrive there the day before departure and leave a day after we get back. I figured out how much to spend before and after the cruise, but as far as on the cruise I am unsure. We plan on living in the moment. So being able to do anything on the ship would be nice. We both drink (a little) and my wife smokes. How much is enough to have a romantic cruise with the misses?