Harmy said:
Plus it's not a great matte-painting to begin with - the background has a bit of a pencil-sketch feel to it - a bit of blur actually help it look more realistic.
Yes agreed the Blur does help it I had a quick fiddle with it.. the only thing that would be worth taking from it and adding would be the actual sky which is what really seems to have got lost in the original composite.
It was not a huge difference after adding all of it.