I have read that a significant fraction of sea level rise is due to the ocean water expanding since slightly warmer water is not as dense as slightly cooler water, which would serve to push the atmosphere up.

The air is warming too, and the expansion of the air will make it less dense, which utterly swamps the effect from the expansion of the water.

That is, the remaining land would have higher value per hectare on average for a few reasons.

Really? I see that the other way around.

Beaches are valuable, and it will take a lot of time or money to make them at their new sites.

Estuaries provide a lot of ecological services and are basically flat. Having them be at the wrong depth will screw up those services.

Many cities (concentrated value) are right down on the water, and it will be muy expensive to save them and enough of their outlying areas that they remain convenient (which was a large part of why they were cities in the first place).