Like, create a hall of fame of good posts that first time visitors can see

A similar idea that I've seen work on some subreddits is a "Post of the Week" thread. You nominate cool shit you've seen in the past week (perhaps via a sidebar link to a thread that's regularly reset) and users vote on what they liked best. Maybe winners get some sort of special username flair, but I kind of like the "the points don't matter" approach we have going. IIRC /r/DaystromInstitute and /r/HighQualityGifs do something like this and it seems like a good way of encouraging engagement.