Depends what you think "dress up" is....What I think dress up is might be very different than what others think. I don't put on a suit and tie for J!
Answer though - no. I always look clean and put together, so jeans, a button down or clean cut polo, and nice shoes is about as casual I'll go.
I never understand people who insist on workout wear when they fly though. There are always swarms of people in yoga clothes that swear it's "comfortable"....How uncomfortable are jeans or slacks?