I had the old Spirit credit card and it automatically paid for the $9 club. Spirit then switched to a different bank for their credit card and now the customer is charged to belong to the $9 club. I forget now what the yearly free is but the $9 fee is usually posted within a limited time and close to the time of the flight and I no longer belong because the flights are inconvenient for my schedule. If you can fly last minute and are going where the $9 flight is going, I suppose it is cost effective but for me, it is a waste of money.
Also with all of Spirits add on fees, the cost is nowhere near $9.