With respect to emails, most emails that I read are actually written by people important to me. You may or may not think my boss is important but I'm going to read his email. It's going to be really hard to find a common metric that measures the non-spam-ness of a person. It's all relative.

Maybe, if you took it to the next level, and said each person has their own custom importance function...

Even then, it's still email (less spam, maybe) and not a replacement per se.