...well, I'm not sure what you consider "dressy". The days of required suits/tuxedos or evening gowns are long gone on Celebrity, et al. Yes, Celebrity will have what they dub "Evening Chic" evenings where the suggested attire is to be nicer than the other evenings, but it is still a long ways from formal. If gentlemen wear long pants and a collared shirt, you'll be fine. If ladies wear dress slacks (or a skirt) and a nice blouse, they'll be fine. Please don't let attire dictate your enjoyment.
The buffet for dinner is a very nice option. The food is always fresh and the variety extensive.
Have a wonderful cruise!
CM