Update (04/04/15): I want to stress that this is no longer an effective methodology. A more modern approach would be to assign a dedicated normal map to each rock permutation and then tile albedo/roughness/specular values across the rock surface in procedural textures.
I decided to put a little additional work into the rocks from before. I was unhappy with the cartoony aesthetic of the previous diffuse map and encountered some distortion when tiling the detail texture. Consequently, I decided to reunwrap the rocks and resolve the distortion issue by using more seams — all of which are near invisible.
This made for a good lesson on the importance of re-evaluating one’s work and making alterations where necessary. The end result is now far closer to what I originally had envisioned.
The second image demonstrates how the rocks can be vertically stacked and horizontally repeated so as to create a rock-face.