The suggestions were still good though, my comment was more to make you realize that there probably wouldn't be a reply from the person who originated this thread.
The multilevel/faceted surfaces definitely help, especially on the surfaces or areas that will be close to the viewer. Often times, you can get great effects by using the 3-D effects near to the viewer and go to more 2-D for stuff in the distance. Once the 3-D aspect is established, people take it for granted that it's all 3-D.
You can get an easy stippled effect using whisk brooms, and or brushes, and a couple of different colors of paint. Laying down a base layer, a light gray/grey in a solid coat over the surface, then, when that layer's dry, use a different color paint, and just dip the tips of the bristles of your whisk broom or brush in to it, then fan the bristles so that they fling the paint onto your object. The more colors/colours you use, the better the effect, but don't kill yourself trying to use a ton of colors, in dim light, much of the color/colour values disappear. A suggestion, start on the back sides of tombstones, crypts, etc. This lets you perfect your new skill on an area that probably won't be seen. Also, try using an old hair comb to fan the bristles on your brush or whisk broom, the individual teeth on the comb make it easier to get a more even stipple.
You can go back with a fine brush and add veins, cracks and fissures.
Getting a book of good reference images for the desired stone(s) can be a major help too. If you want to sculpt using paint, get really good with fan brushes, and or airbrushes. The latter make that kind of work a snap.