On page 5 of the rules reference it says: "The attacker can spend this icon to choose one of the defender's defense tokens. The chosen defense token cannot be spent during this attack."

What if the attacker does not choose to spend the accuracy icon to preempt a defense token? Can he spend the accuracy icon in some other way, perhaps to cause damage?

Simply...no. The Accuracy icon is specific in its use. No magic here...yet.