Unlike most of you, I live in Europe. I now prefer not to take cruises I cannot either drive to or take the train to. But here is the problem: If we drive, then weight of suitcases is not a problem. If we take the train it really is since we have to carry them on and off the trains, make connections etc etc.
While I personally love formal occasions, I really think formal nights should be restricted to sea days and not required at all in a very port-intensive cruise. My husband wears a dinner jacket to the formal nights. I don't really want to take this on trains and neither one of us likes spending the time to get all dressed up when we have just come back on board from an all-day excursion!!
So I would vote for "Elegant casual" on all nights on Mediterranean and Baltic cruises, and Formal nights on the Trans-Atlantic crossings and longer cruises with sea days.