I'm one of those who believes that people should stick to the suggested dress for each evening, and abide by whatever dress code is published.
I don't know how many of you live in a world where you go to social events that aren't aboard a ship. I do. The invitations frequently state things such as "Business Attire," or "Casual," or (horror of horrors!) "Black Tie." It never occurs to me to think that I should dress some other way. My tux fits fine, as do my other clothes. I'm comfortable in all of them. What on earth is the big deal about simply adhering to a dress request? It's one of the elementary social graces, and is not a difficult thing to do. As Kuki said very well, it's easy even for people who don't normally dress to outfit themselves perfectly well for a cruise for very little money.
And on cruises, it's perfectly easy to do a little research and find a line that doesn't require "fancy" clothes, if that's a big issue for you. It's no secret that some lines are a little more formal than others.
I would never consider showing up at a black tie event in a sport coat, or at a business attire event in Dockers or jeans. I dress as requested to honor the spirit of the event, my hosts, and my fellow merrymakers. I don't spend time worrying about what I can get away with, because it's perfectly easy to jump into clothes that fill the bill.
I enjoy being with ladies and gentlemen who don't feel a need to make a "personal statement" by dressing down. I find that dressing appropriately is a sign of maturity and I honor that.