Are you thinking about adding a "light direction" to the blocks instead of just shaded all around?
Here's my two cents:
The dirt and stone are shaded on top, a shadow is cast by the chucks above it, as well as on the bottom, from the light above. If I didn't shade them on the top, to say, they world just look like staggered spikes of dirt, not soft clumps. Under a 16x format, there is only so much room for one pixel to discern one clump from another. I don't like leaving much open pixel coloring. The same goes for other textures, like bricks. I'm not going to make every chunk of dirt or every brick a 45 degree angle gradient, I want the colors to blend smoothly into each other, while still maintaining contrast over all colors in the texture.
Also, you can't always just think of a texture as the side of a block, Most textures tile around the block encompassing the sides, top, and bottom. Since I can't edit all sides of the block individually, I have to make a texture that will look correct on all sides. This current type of shading might look like the top of a block, with light from above focused on the center of each chunk of dirt or each brick.
"Pillow-shading" is called pillow-shading because the light is focused from directly above, and it doesn't look good in most pieces of pixel art, where the perspective is usually from a side view. Minecraft is 3D, and textures are not only displayed from one angle. They are twisted, turned, flipped, and cut. If you want something with a definite light direction present on every block, use Tiny Pixels. I'm not doing any "highlight in the top left, shadows in the bottom right" kind of thing.
Just wanted to let everyone who's interested know that I'm working on another texture pack for Peytonisgreat's palette challenge for May, so work on this may be slower for a few weeks. I will release a download when I finish it.
Good thinking. I touched up that big stone, but I'm still not going to use it, because it doesn't even remotely go with my stone color. I think that I need bigger stones for cobblestone since my stone is already segmented into small chunks.
Edit: Badda-bing! Fixed up dirt! No more super-shine or unusually large chunks!
Edit 2: Just updated the O.P. with new screenshots in real environments.