We have had ours for about 5 years. When we redo our room in a couple of months we are getting a new one, only because we are going from queen to king. I always keep a mattress pad on it so it's clean. So the queen bed will be going to my 9 year old DD.
I use peroxide, baking soda and water. Let dry and then vacuum. It looks clean but the thought of laying on the same young for years and years grosses me out. Even with the sheets and mattress cover it just seems dirty.
We change every four years, not because ok kids or stains...just because we want to. You're spraying it down? What kind of mattress do you have that you can just spray it?