A little number next to each question to be able to tell which questions have been answered.
Or in related only appear questions answered with upvotes already?
This is a good idea. It will also improve the look and feel... Right now we have a list of lines on the right side, not very sexy.
Give extra reputation for answering a question with upvotes appears in the Related for this very question and has -3, so no, downvoted questions appear too.
Perhaps a color-code? Similar to the way the #-of-views text color changes (subtly) under questions listed here.
So the most-viewed (or most-voted) Related questions float to the top, in a color-coded fashion. Color code could even be based on a combination of views, votes, answer status, etc. This might be more subtle than a number, but I think that's the beauty of it. It's an easier way to view the information.
It's worth considering to include up to three numbers:
Or at least pick the "most important" one, then display the others in a three-line tooltip.