I've dressed up for a Baja cruise on Celebrity and another one on Carnival. Both were 4-day cruises, and we took the train to San Diego for the Celebrity cruise and drove to LGB for Carnival.
In July we are taking HAL Zaandam out of YVR for a northbound Alaska cruise, then 5 days to the interior of Alaska in a rental car. We are "dressing down" by choice. Why? This 2-week trip will require formal wear, hiking boots and jeans, wet weather attire, shorts, mountin biking gear, swimwear, and everything in between! My teenage son and I are both very active, but handling lots of luggage through baggage claim, gangways, rental car shuttles, stairs, buses, etc. is never fun. I can't tell you how much time we've saved by being able to catch an hourly train just in time, get in on a tour, breeze through Customs, or be at the front of a line by traveling light. Also, all the stuff has to be stored somewhere in your cabin. (Why do you think they call it "lug"gage?)
Sorry about the tangent....for Alaska I'm dressing "resort casual" and maybe throw in one dress shirt, sport coat, and tie. I will do laundry halfway through the trip to help cut down on packing. If we realize we have taken "dressing down" too far, we will simply use the Lido on formal nights. More out of respect for decorum rather than worrying about what other people are wearing.