Thanks Kirk,
Reading this over, several observations come to mind. This procedure does not seem purpose-built for dealing with the problem of film "grain", which may have different characteristics from the subject matter of the retouching it appears to be purposed for, though not having done it, I don't have a view on how much of an issue this could be. It would appear to require case by case fine-tuning to work properly, which could pose a time conundrum for those doing large-volume scanning work. The distinction between image detail and so-called "grain" can be tricky, especially when dealing with naturally "grainy" surface textures. I can see the distinctions being difficult, yet that would be an essential element to successful separation. A bespoke application such as Neat Image allows one to easily identify and mitigate noise or "grain" by channel (Y - luminance; Cr, Cb - the colour channels) and by frequency (High, Medium, Low), allowing the user to decide in real time (as it recalculates) the level of adjustment for each at which image detail may begin to suffer. On top of the quality of the results, the ease of use of the interface and its responsiveness is what attracted to me to this program in the first place. While it may seem counter-intuitive to sharpen before "grain" mitigation, the advantage of working in this manner allows one to see in a post-sharpening context at what point the right degree of acutance of real edge detail that one achieved from sharpening could begin to suffer from overly aggressive "grain" mitigation in one or more channels or frequencies.
(You will notice I have "grain" in "", because when dealing with colour fiom it's a generic name for what may be so-called dye clouds that are formed by clumps of fundamental silver particles and dyes through nine layers of emulsion.) Dye-clouds are much larger than silver particles, not as sharply defined and come in random shapes, posing perhaps a challenge for distinguishing them from image detail and reducing their visibility without destroying real detail.)