We used boatyball at Cooper and like being able to sail with no hurry to get there.
I also witnessed at great harbor on Peter a boat leaving in the morning without paying. The guy collecting fees had to run him down as he was leaving harbor.
I see advantages for the owners of the mooring balls getting paid in advance. I like being able to pay with CC instead of cash.

As for adding more balls, I think many harbors are too full of balls and leaves very little area to anchor anymore.