I think you're discounting that most people really don't want to live on a boat. An alternative is living in the countryside, but most people don't want to live there either.
It's not just materialism or a status symbol at play here, but the preferences of the majority of society pushing people into zero-sum. If people suddenly decided that living on a boat isn't that bad (not going to happen), then the price of docking your boat in the middle of Copenhagen would be through the roof in short order. Still zero sum.