on a 7 day cruise you will have 2 formal nights and that's it. The rest of the nights the dress code is " casual nice" capris and a nice top, with flat sandals would be perfect. Don't miss out on the dining room experience because you think you have to get all glammed up every night. As for the formal nights - a long dark skirt with a dressy blouse, a dressy pantsuit or a nice cocktail dress would be just perfect.
Formal nights in the dining rooms are extra special, a lot of fun, an event actually.
Just think about it before you automatically dismiss the possibility.