Dantes (aka SquireKev) has put up video and picture comparisons with RB3D using a custom DX9 plugin called ENB Series FX. There is definitely a subtle difference, but I'm not sure it's any improvement. Check out the full-rez picture comparisons and judge for yourself!
One thing to note if you want to install it: it's not compatible with the OpenGL wrapper! However it does work with the DX DgVoodoo Wrapper.