In response to getting a kitten when you already have a two year old cat...I have experienced the "this is my territory" destruction. He stopped using his litter box in response to my feeding of outside cats. The cats were not even in the house, but he could see them from the window.

I agree that adding a kitten with a kitten is great. I am a strong believer in cats/dogs having someone to play with when their real entertainment (having us serve them) isn't available.