Dust and grease can affect photographs whether they are on a filter or a lens. I would rather clean a filter and discard it when its coating gets worn then replace a lens when its coating gets warn. YMMV. If you are independently wealthy then this comment may not apply to you.
My post was in response to the apparent confusion here between the effects of low quality filters, and the effects of dust and dirt. In my somewhat unclear manner, I was trying to make it more clear that the effects are different, and should not be confused.
I agree that there is a real practical advantage to filters, as long as they are carefully chosen and maintained.