if i understood correctly i have the same problem where its difficult to tell where one wall starts and the other ends. Only thing ive found to help is to move the texture on the x or y axis a lil bit to throw off the seemless apearance. Heres a couple examples of bumpmapping in gimp.. not really the same but might help

with out bump mapping


with bumpmapping


without bumpmapping


with bumpmapping and color adjustments


Now since this is only 2d its not really the same but notice how the grout appears more imbedded into the tiles with the bumpmapping. In a 3d world this would be dependant on the way light reflects from the object and make it appear as tho its higher detail then just a flat block with a texture on it hope this helps

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