There's a very powerful technique for haze removal out there. Unbelieveable amount of haze reduction in otherwise useless image.
I can't even come close to writing a plugin to do it, but would sure like to see one available.
There are some example images at:
http://danalstadt.org/post/2010-05-06/final-project
Graphguru
Try Dup, color to Alpha and
Try Dup, color to Alpha and then on the Top layer, add a mask to reduce the effects on the most dark parts of the image so the result won't be too dark. :)