The grain of the image has a photographic look, it does not look like the usual GC noise. It might work very well as it is (make the whole thing black and white and then sepia/bluish silver color it and you have a 40's or 50's photograph) or it might be manageable with programs like NeatImage.

About rendering: a mad proposal for geekiest among us. Lux is available also on Linux and does not require a graphical UI. I have seen reports of people making personal supercomputers out of clusters of cut-to-the-bone motherboards with Linux installed with price tags less than 2500$...

Another alternative, when Lux will have a good support for CUDA, is the option of making a dedicated PC with 3/4 nVidia graphic cards with high-end processors; it is not a demented proposal, I have described nothing more than a high-end gaming box.

GIMP 2.7.4, Inkscape 0.48, Genetica 3.6 Basic, FilterForge 3 Professional, Blender 2.61, SketchUp 8, PoserPro 2012, Vue 10 Infinite, World Machine 2.3, GeoControl 2