Since the ship has a dress code for certain nights and hours of day, then it is a 7-8 for me that it be enforced. For every person who is excited about the opportunity to dress up on formal night, there is at least another one who tries to get by with the minimum. If the cruise line doesn't nicely reinforce their standards, then people learn it is not important if they don't follow them. And if the dress code is not important enough for the staff to reinforce it, then get rid of it or keep it to a bare minimum.
I know I sound rather rigid, but I tend to be one of those people who follows the rules and it bugs me to see other people get away with breaking them.