The way I see it, the less you know about your enemy, especially their plans, the more reason for you to be extra prepared. You dont go striking down the enemy until you know full well what they can do, and even if you know your enemy, you still dont know everything about them, leaving more reason to prepare as much as you can to take them on. Kairi will be needed for this, because if Sora and Riku could handle it all, then what the heck are the King, Donald and Goofy around for? And why have Kairi use a keyblade just once if she's not gonna get the chance to help her best friends?