For example, there are a lot of duplicate submissions, users tend to herd around top submissions, etc.
One thought is that randomly users are presented with a mix of new and top stories and requested to say if each story is new or a top story.
Reference to dups provides proof that "top" stories are being missed, since one dup might have 100+ upvotes, while another will have just a few upvotes and no comment saying it's a dup; meaning to me the only difference is the volume of comments/votes between the two.
Beyond that, I've seen research that shows seeding a submission with even just a few comments/upvotes greatly increases the odds of future traction.
Point is to reduce noise to signal ratio.
You want to ask users if a story is new, so that they check a timestamp manually and maybe even report correctly?
That's inane.