I have not. I always kind of looked at that as a “last resort” sort of move, but if you are smart about it, it probably would make sense if you can get a percentage back. It might also be cruise line-dependent, as I thought some cruise lines actually charge you a percentage of whatever you put on the room.
As far as “declaring $10,000 or more” being a potential issue, I’ve never once had that cause a problem. They’ll ask, and I’ll just say “no,” which is probably what they hear every time. Yes, it can be a little awkward carrying that much money around, though it’s often useful if I’m going to places with big casinos where I’d want to have that kind of bankroll (Bahamas, Puerto Rico, Aruba, etc.).