I tend to chain selectors as little as possible in plain CSS, so I generally don't run into having to read huge chains of sub-selectors.

I will agree that heavily-cascaded stylesheets are practically impossible to read. Writing styles in a way that reduces your need to create long inheritance chains feels like a more flexible option (not so tightly dom-coupled) that doesn't require a "style model", though.

How do you handle adding the same styles to page elements that aren't siblings/exist in vastly different areas of the dom structure?

Mixins could probably do it, but writing too many of those would open up new problems.