You're right, you'd have to be a stacking algorithm connoisseur to appreciate that. I just thought there's too much visual noise in that render to discern anything useful.
I'm not sure what you mean by constructing a smooth depthmap and painting details on it and I'm afraid it's not common at all.In computer animations, it's common to construct a smooth depthmap and then paint some detail on it. This greatly simplifies the process of constructing the model, it makes the animation run a lot faster, and it often looks pretty good. But all that just makes an expedient approximation, not an accurate depthmap.
Depthmap is also rarely used in animation except when the depthmap is created procedurally and often for a very basic animation such as faking the moving surface of the sea where it is much faster than true simulation and still looks good.
Apart from engineering, architectural and medicinal visualisation, accuracy isn't really sought after in 3D, and where accuracy is a must, depthmap isn't really the first thing that comes to mind since it's still only an approximation created by a software as well as being 2D.
Funny enough, in 3D depthmap is often used only as a render pass to fake DoF in image editing software like Photoshop.
Well, anytime you want to check the accuracy of a depthmap, feel free to PM me.