For me if there is a .pz2 file available to use, I use that. So a .mc6 file would be just redundant to me.  Also, you need to take into account that not everyone knows how to use the material room, or even wants to use that room at all.

I like continuity of naming between folder directories.  For example it drives me crazy to see a package unzip with a folder named "Red Dress" in the character folder and a folder called "J Jones MAT" in the pose folder. IMHO the folders that unzip should contain not only the creators name, but also the outfit name too and it should be congruent throughout the library. IE:  "J Jones - Red Dress"  or something similar in all library folders. 

I prefer the geometries and texture folders to be named for the creator with a separate folder inside for the outfit. This means that if I have 10 outfits by "J Jones", I can look in the geometries/textures folders for  "J Jones" and find all 10 outfits in separate files inside.

I like the readme file to be named something other than "readme" and I like it at the same level as the Runtime folder, not inside it or placed in the props, textures, geometries etc folders.

If a package is being made for more than one figure, I like it very much when the creator places the files in the Pose library in separate folders for each figure, this way not only do I not have to  dig through a long list of files and delete the ones I don't want, but it makes it easier for me as someone with dyslexia.

If a package is meant to work for more than one version of Poser, I appreciate it very much if the files for each version of separated for the same reasons I listed above for the  multiple figures.

Hope that helps :)

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi