The shape of the various structures should be making most of those shadows. Having them burned in like that almost always makes it look like dirt rings, like the model hasn't bathed in quite a while, because they don't change as the model changes position or pose. 

The healing brushes in conjunction with the dodge and burn tools could help a lot with that. 

If you're texturing for a video game then you'd be more likely to burn in details like that, because game characters are too low poly to really build a lot of those structures, but not for poser-ing. 

 

~Shane