Actually less for two reasons. One is that new land isn't created to replace the lost, so you lose area to both rise, erosion, etc. Second is that the new shore isn't necessarily going to be viable for use as property, as much could be eroded or swampy or whatever.
But this is just stupid. At least Lex Luthor had a plan to capitalize on the changes to turn cheap land into valuable, Trump is just making things up as some excuse to create a positive and not do anything.
Technically he's right just in the bad contractions of capitalism way. Just like when excess food was burned during the depression, shifting coastlines would create completely new real estate speculation opportunities and new displaced buyers
One of 's fellow sex predators played the part of Lex Luthor in Superman Returns and his scheme to use Kryptonian technology to increase the value of his property made more sense than that.