The final snow shaders I shared don't use luminosity anymore either, Dune, it was far too much trouble keeping it controlled in the shadows and, it really wasn't correct anyway to use luminosity for snow-glinting.
The sparkles now are from reflections via tiny(1mm scale) perlin dots over the entire surface, they still only glint in direct light, though.
It's probably much the same idea as your stones method.
I should probably re-upload them, since I'm an idiot I haven't put them back here yet. I'll do it shortly...
