Pauline
I have been on many JY tours to America, and two have included NYC..
Just you tours are very busy in the day, and I can assure you it isn't dressy in the evenings, I go for comfort in the day and if there's time to change smart casual for the evening. really just go what you comfortable with, some people of course like to dress up more, as long as I am comfy that's what matters to me.
I was last in NYC in September 2014 so if you have any questions just ask.
Cindy