I used to take a suit and dress shirt on all cruises but now I don't bother, especially with fly-cruises where they take up so much extra space and weight in your case. The trouble with a "dress to impress" dress code is that it's very much open to interpretation. I just wear smart trousers and a collared shirt for dinners each night, including dress to impress nights. If they stated "black tie" and enforced it, I'd be happy to oblige.