Even after stacking dozens of subframes to reduce noise in an image, I would still have quite a good deal of luminance and color noise. Luminance noise is definitely the most distracting, and removing it without removing detail of approximately the same scale was very hard to do manually. After researching the topic a good bit, I found a mention of the Gimp G’MIC plugin called “Iain’s Noise Reduction.” This filter is incredible!
There are separate settings for the luminance and color noise reduction, which is really nice. In the “13 Preview Shows” setting dropdown, you can switch between the effect applied to the image and showing the luminance and chroma noise it detects based on the respective settings.
This allows me to exactly fine tune the noise reduction so that actual noise is included, but fine details in the objects are not smoothed. You can also cull the chroma noise blotches without losing actual color data within the object. I don’t tend to use the despeckle option, as I feel it smooths out larger, similar color areas too much.