okay a bump map works off the blurred grey color values between black and white (rgb 0 -255)

White is the high point ( upper most surface) while black is the lowest point (cracks) . The map is essentially a texture map that gives the effect of a bump in what is a flat surface. It just the refraction of light that give it an embossed feel in the render. so even if you turn the model around and look at profiles you will still get a flat surface.

Normal mapping is similar but works of high resolution geo to be turned again into a texture...but the difference is it works of the surface normals or its vectors depending which way the surface is facing giving you a better sense of detail...but again if you rotate the model in the render the geo is still essentially flat. The normal map is better than a bump but still works as a 2d texture but with a greater output

If you want to do it where it doesnt look sprayed and more defined then either do a displacement map or model in the extra geo. I dont think it will hurt to add the geo at the end of the day - if you are sensible with you polys....

Jay