However, my moorings are allocated on a waiting list basis. There are vacancies on the mid-river ones & a 3 year waiting list for quayside berths (no need for a dinghy or waiting for the tide). Once you have a mooring you keep it as long as you pay your biills. If you aren't using it, visitors can.
That's how it works in Kirkcudbright Marina. I have just paid my last bill there for my old boat and will be asking to go back on the waiting list in case I fancy keeping the new one there in the future. Waiting list length is draft and depth dependent, but generally somewhere between ten and twenty years.
Reallocation each year would be a bit awkward, as a "pontoon" boat might not be suitable for other moorings: at Kirkcudbright you dry out if you are not on the pontoon. Selling some berths on long leases seems a reasonable way of funding things.
I was a member of a gliding club which built a hangar for private owners' aircraft with mixed funding. Some owners bought a permanent share (a hangar bay) for something like £10k down, while the Sports Council funded the other half of the building on the condition that it was to be available to all members through an annual lottery. Once all the committee members had obtained places, however, the lottery just didn't seem to happen any more. Which was odd.