I just tried a "raytrace everything" render and it still comes out with the banding. Didn't seem to make any difference at all.
The image I posted was from a saved EXR opened in Photoshop. I added the text/arrows and saved it out as a PNG. In the most recent render the banding was visible in the render window even before saving a file.
I also just did another test render with Detail at 1 instead of 0.8, atmosphere samples at 256, and sample jitter at 16. The results are attached below.
In looking at the render settings, what does Detail Blending do and might it help? Currently it's set to 0. Scratch that, I tried it at 1 and there's still banding.
I'm running out of ideas here other than turning off the haze glow completely. This totally changes the dynamic of the image, though, so I don't consider it a realistic option except as a last resort.