Mushishi is kind of a hard show to collect from. There's only 1 recurring character, and really, how many drawings of Ginko do you need? He's not exactly the most charismatic anime character. The rest of the characters are generally not that memorable or compelling either. There is a sameness about them that makes it hard to even identify which episode they're from sometimes. It's really the very imaginative stories that are the true star of the show. And the most memorable art is surely the gorgeous backgrounds.
That said, I still really enjoy the sketches from Mushishi. I'm a big fan of rough drawings anyway, and it seems they don't get much rougher than some of these! Take a look at the first 4 drawings; they look like they were scotch-taped together from fragments fished out of the trash can! There are even drawings on the back that are completely different from the ones on the front. It's almost as if everyone just met at a local bar and drew the thing up on cocktail napkins! That's it!! Mushishi sketches are from the "Cocktail Napkin" school of anime! Well, just kidding, but still, this seems to point to a rather messy and chaotic production process.