1) Why not limit submissions on HN to one per day?
That way, people will only submit their most relevant links. If a story is important enough, then either 1) someone else can submit it and this will invite broader participation on the site, or 2) it won't be submitted today and can be added tomorrow (and it probably wasn't that important to begin with).
2) HN articles used to relate to either hacking or startups (stories about education, economics, etc. were typically found on Digg and Reddit). Why not return to this formula?