We were on Regal for two weeks in the Med this summer. Club class dining.
First formal night I wore a DJ. Many others did as well. Dress to impress night - I wore my other DJ. But I was very much in the minority. So, I think, in reality, Princess have gone down the one formal night per week cruise week. But, we are on Sky out of Southampton in April, and with more Brits on board, the dress to impress night will be more formal.
I'm really sorry, but I have no recollection of the menu offerings on each night, apart from the beef carved and served at your table, which was excellent.