I like Dave Pell's Next Draft, which is just interesting general news stories, and also Azeem Azhar's Exponential View, which covers tech, with a slant towards AI/ML. In terms of stuff the HN crowd is less likely to already know about, I like Archinect, which covers architecture. It's not really a curated article roll-up so much as it is an architecture news site, but their weekly email is a nice way to stay on top of what's going on in the field.
I used to sign up for an HN newsletter that'd only show the top posts. I thought that was an effective way of pushing only the best content to me every few days. Realized later that I enjoy reading a some articles that didn't get a lot of upvotes.
I also tried to create an open google doc where a small group of friends could share links to articles they found particularly noteworthy. Participation was 0, so I gave up and now just store interesting articles in my bookmarks folder. Messy.
The problem is getting it to the optimum size. If it's too small, it won't work because nobody will want to post. If it's too large, then the signal-to-noise ratio drops and it's no better than Reddit or HN.
Also, moderation is hard.
I think the best solution is to find one or two people who know their stuff to curate everything. Add community engagement mechanisms incrementally. For example, enable social media sharing and commenting before account creation, upvoting, and article submissions.
Wonder how a Quora/Medium model (invite-only) or The Information (paywall) would work for newsletters, since content isn't original?
I think the stuff I line most on HN doesn't always correlate with what has the most upvotes, so I don't think I'd be happy with a best-of-HN summary either.
Are there any email newsletters you already subscribe to and would recommend?
I found some of the human-made playlists on 8tracks.com to be better than a lot of the algorithmically generated ones on Pandora/Spotify/Youtube, but music is highly subjective.
Been meaning to give product hunts collections a solid attempt:
For book recommendations, I find an intellectually-minded friend on Goodreads who has similar tastes to me, and just go down his/her list.
I think a general pattern here is: there are positive deviants in society whose tastes and interests correlate with my own far stronger than the average's.
Great original question, BTW.