I have never taken a cruise before and see that the clothing recommendations are casually elegant for dinner and formal on two evenings. I really don't have any clothes that fall into category because I dress for comfort. Besides, I don't want to haul two wardrobes with me from the US. How important is it that I follow the clothing recommendations? If I want to come to dinner in my comfortable pantsuit, will they refuse to seat me?

In different tours we took, they did not any problem at fine restaurants in hotels or cruises, if you do not wear a Tshirt , shorts or Addidas.
However, are restaurants where a jacket is required for men; sometimes the restaurant can give one to whom has not one.

From my point of view, the problem is how you feel if all other will be formal dressed and you will be too different.

I suppose that a nice top and black pant are OK.

Have a nice trip!