There is another filter I can offer. It’s a godray filter. I was really willing to make like a showcase demo before giving them all out to public, but I guess - eh! 
This is it, I hope you can figure out from the file how to use it. Good luck with making things look even better. If you need help with setting up materials, don’t be shy to contact me, I’ve experimented a lot and have great shading, lighting and other rendering-related thing knowledge base and experience. 
Godrays.blend (486.6 KB)
Also, I think that the AO you’re using could be smoothed out a bit by using low-bias mipmaps.