So, I've picked out the model buildings for the background - now it's time to try and get the original fuzzy image into something a bit more usable. I used the Filter -> Other -> High Pass filter with the 'Hard Light' layer type. That seemed to produce the sharpest image. I also played with the levels and managed to go from:
Which I'm not too unhappy about. It's not perfect, but I think it's okay for this purpose. So the last thing to do is sort out the composition and pull all the elements together.