An anchor ball, or inflatable, is particularly good when you are running solo and need some helping "hauling the rigging", but is not typically a sailor's first choice.
Keeping a ready spare has its price, as it doubles the maintenance costs. Units will require more attention as they age, whether you use them or not, and will eventually become obsolete. Better to keep just one and then replace it when the performance is lacking. Get a newer, stronger model that can handle the additional weight that's been added to your 'console' and 'bilge' all these years. And remember, its often less expensive to order from overseas than to buy locally, even after you figure in shipping.