I suppose that could be the case with a private marina who sees full slips and a waiting list as an excuse to jack everyone's rates up more.
Many of the marinas around here are city-owned and as such their rates are set by marina costs vs marina income or city tax revenue or both. So if all the slips are occupied, that's great and it doesn't matter if there are 500 boaters on the waiting list, this does not affect moorage rates. And of course the marinas also get income from the businesses that are located on marina or port property and pay rental or lease costs.
What does affect moorage rates are increasing insurance costs, required (environental, safety, or otherwise) improvements or changes to the marina, expansion of the facility to accomodate more customers and generate more revenue, the continuously increasing labor cost of marina staff, vendors, and suppliers, and so forth.
But...... if the slip vacancy rate goes up, then marina revenue goes down. But their costs don't go down. So if the vacancy rate continues, the growing deficit between marina income and marina expendatures has to be made up somehow, and one way to do that is raise moorage rates.
So a full marina around here is a great thing for the marina tenants. What we don't like to see are long term vacancies because that's one more upward driver of moorage rates.
I agree with FlyWright. Whether a specific boat is used or not makes no difference whatseover to someone else's moorage rates. If it's there, it's there, and its potential effect on rates due to supply and demand is not going to be changed by how much the owner uses it. If he takes his boat elsewhere or sells it another boat will take its place and nothing will have changed. The slip is sitll full, and the waiting list is still there.