[Plugin: Polldaddy Polls & Ratings] Restrict to registered user only

You can, but you’ll need to do some coding. Check is_user_logged_in() to make sure the user is logged in. If they are then use remove_filter() to remove the polldaddy_show_rating_comments, polldaddy_show_rating, polldaddy_show_rating_excerpt and polldaddy_show_rating_excerpt_for_real filter actions.

Check the end of ratings.php for where those functions are added to filters.