If thats an issue, I'd start from scratch and redraw the hexagons just long enough so that you can make that texture a power of two... I think the problem is that these hexagons are longer than they are wide, and so a power of two will not fit them without cutting it in half.
Or... you could come up with a creative way to cut them in half and make it look normal. Either way, its a pretty basic texture and so it shouldn't be impossible to start from scratch. I wouldn't try to stretch the current version though.
Do you use Photoshop or GIMP? I'd try drawing the cracks on a different layer, and changing the opacity so that the color is influenced by the colors beneath it. (you'd have to switch to RGB for that... to switch back without losing the color, just select the area around the cracks, invert it, and merge to a copy of the background... you might keep a copy of the cracks layer too to make it easy to repeat the process) Try shading around the cracks until it looks like they really do cut through the texture. Meanwhile I'd recommend that the cracks not be too visible from a distance and that you make them less dense.
I'd also sharpen the main shading, on a small color range I usually go every other shade... the larger ones generally vary. The shading from the cracks can and perhaps should be more subtle.