(possibly insane) Idea : Open-source the Hacker News code. You have a self-selecting community of hackers. I'd bet some of them would work for free on the site. It is easier to review patches than create them!
I think it's a bit odd that the hn source is only "semi-open" (see my comment below). Having it as a working open source project makes sense to me -- it'd give Arc a boost, and give the world a forum project that is well tested in the real-world.