It won't make a difference, apart from file size (which should be neglectable).
I would make the stretched/tiled ones smaller, because they are repeated anyways.
You could also remove two of the corner pictures (leaving only topleft and bottomleft) and then mirror the textures in WoW:
texture:SetTexCoord(1, 0, 0, 1) would mirror it horizontally. I often use that because I'm too lazy to mirror and save them in my image application.
But that's just the web designer speaking in me - where file size matters