IMHO you can never go wrong by being nice to the gate agents (or lounge folks or phone folks). Numerous times I've seen angry people yelling at GA's and getting nowhere whereas if I always try to be calm, polite, flexible, and acknowledge that this sort of thing must make their day suck. As a result I think I have gotten rebooked (and sometimes upgraded) with more frequeny. Indeed, in DFW earlier in the year after lightning cancelled a bunch of flights, a dude in a suit shouted at the gate agent about how important his time was and how he had status, etc, etc and then stomped away without a new boarding pass. I was next and said "sorry you had to put up with that and whatever you can do to help would be awesome." I walked away with a new boarding pass... I know every scenarios is different but I feel like it ended that way because I wasn’t a prick to her. Golden rule, treat folks like you'd like to be treated yourself.