One idea I played around with is using "world UVs" instead of directly UVing each voxel cube manually, so that your materials can be higher definition and less repetative... the idea is that when you generate each voxels faces you also generate UVs for the face based off the positions of the vertices in the world and the normal of the face - so if it was an upwards facing voxel-face with a normal of (0,1,0) then we could discard the Y values from the vertices and use a new Vector2 comprised of the X and Z as UVs. Now your materials can spread across multiple voxels automatically, and you can also include secondary offset textures overlaid over the top at a different scale with dirt or cracks or whatever to help it look more randomized.

Another idea is the faked ambient occlusion stuff - it won't help your textures at all but it really does help improve the visual depth of your voxel geometry.