Good glass is expensive because of the glass and the elements that are used. You get what you pay for in terms of sharpness, contrast, and build quality. How bad is the blemish on there? Does it affect your pictures? If it doesn't, I'd just keep it...it's a very good wide range. You do realize that the 70-200 is going to cost as much, if not more, than your 10-22 right? I know the 70-200 f/2.8 is about $1700 for either the Canon or Nikon equivalent.