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.
Steve
Steve:
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.
As to independent wealth, I remain in hope...
Matt