I recently invested in the entire keying suite from Red Giant and Primatte keyer is one hell of a tool.
But the Composite Wizard has this plugin called "Miracle Alpha Cleaner" which I just used for the first time a couple days ago and it was absolutely a miracle! It took all the remaining haze completely out, leaving me a beautiful key.
Teddy's comments are about the best you can do with Keylight. The contrast is about the best part of the trick.
Eric