Port days factor into our planning as well. If you are going to be doing port excursions all day, then you are not likely to be onboard using the drink package as much. We find it more valuable on sea days and port days when we stay on the ship.
That being said, I think the real benefit of the package is the carefree, all-inclusive attitude it promotes. When we don't have the packages, we buy fewer drinks because I am constantly thinking "Do I really want a $10 drink right now," or "No, I'll wait and get a glass of wine with dinner or a drink at the show later." With the package, we just always say "yes!" Without it, we certainly consume fewer calories
, but it's just not as relaxing. I like to try different drinks, so having the beverage package means I can order whatever I want, and if I don't like it (or happen to get a bad bartender) I don't have to ask to have it remade or anything semi-confrontational. I just leave it and order a different one! May not sound like much, but it is a whole different attitude onboard!