Sorry for the restriction on post pro, but this is a LuxRender competition not a Gimp or Photoshop competition. My best work today wabi-sabi looks much better after even some mild post in The Gimp. But, then I could airbrush out fireflies, or photoshop in something from a real photograph and cheat. With that being said...I would like to make a challenge to all the developers out there. Lets see if we can add some of the open source tonemappers that exist out there. Or how about a simple levels control. I find the levels dialog in Gimp to be quite powerful. That alone could drastically improve some renders. Because, much like a real camera, LuxRender is subject to creating color casts, or having a less than ideal contrast every now and then. My wabi-sabi render had both.
There you have it. The gauntlet has been thrown. We need a levels adjustment in LuxRender. But make sure its applied post render, like the film response. Which in some cases provides a similar result.