I've intimated this in quiet ways over the last while, but I might as well go on record as saying that I think the current trend of painting uv-mapped wear and tear onto everything is an enormous waste of time. I've tried various methods of making the process more automatic, but it's all pretty crude.
On a whim, I decided to visit the site for Modo, and lo and behold, these folks now have what they call an occlusion layer.
[link]Yes, yes, I know that we've all had ambient occlusion for ages, and I also know that it's possible for different programs to bake an AO solution to a texture. What's cool about the Modo solution is that a few clicks can customize their occlusion solver for various looks (like weathering on pits and/ or bumps, top-down weathering, etc.) You can randomize things, bake the solution to a texture, use that texture as a mask for painting rust and dirt, and all that good stuff.
Of course, with this development, the CG and games industry will now decide that "dirt = real was SO first decade" and make everything look pristine...
Anyway.
If I'm not officially on record as having said it, here it is:
Dirt and damage on 3d models ought to be a procedural thing.
However - please note that all of you UV-map painting wizards who can do this by hand and make it look good still impress me.
A lot.
Now...I wonder how I can replicate some of this functionality in Blender...
What I dig about this is that it automates the tedious stuff that does follow "natural rules." A texture artist that can marry the two techniques should be able to do some pretty "bang up" work with less time sunk into the boring parts.
Shame others did not take notice
Maybe the world just wasn't ready for "real is dirty" back then.