This might turn out to be a hugely unpopular idea, but how about favoriting posts? I wouldn't like to see them raise the "status" of a poster or anything - just a little click to indicate to the poster that you liked their post, for both the poster and others to see. The way I imagine it is there'd be a "Favorite this post" button in a corner of the post, next to which would be the number of favorites it's gotten. Clicking that number shows who favorited that post and when.
Also, and I know I've brought this up before, but a "remove from activity" button for the Unread and Replies page would be good - a checkbox you could tick next to a thread title on either of those pages, and then press a "Remove selected from activity" button at the top of the page, so that you don't keep seeing this thread pop up in your Unread posts or Replies page.