This post has been written in someone's suggestion thread, among the answers, so I think it is staying there rather obscured and I should repeat it in a topic in its own right, for getting more attention.
Let's give tools to the owners to turn their ports into attractive places for visitors, no matter if to their clan members or others. How could this be done? By upgrading ports by a selection of buildings there, which produce advantages the visitors want to enjoy, or buy special things there due to those buildings. And with every turnover by visitors, the port becomes more profita