My humble suggestion(s) to make "favorites" more useful (and hopefully more used):
1. add the ability to "favorite" from the front page. I rarely "favorite" anything, because I grew accustomed to using "upvote" as the mechanism to save stories. I would switch, but that extra little bit of friction of needing to click through first, means I stick with my old habit.
2. Add "favorite" for comments as well.
3. (maybe) - consider renaming "favorite" to "save"? Possibly people who are used to seeing the "save" link on Reddit would find that more intuitive.
I'd cast my vote for promoting it more, it's a pretty handy feature (at least for comments)... I also like that it lists things in the order of recently favorited rather than chronologically.
Pinboard [0] solves it for me. I tag all the interesting stories with "hackernews", so I can easily go back and search.
I noticed over the years that my use of Pinboard is very asymmetrical: I save several URLs every month, but retrieve at most a handful per year. But knowing that my memories are safely stored gives me peace of mind (and, just to be safe, I make a backup every year or so).
I use org-protocol-capture[0] (in Emacs) along with Syncthing to push my .org files to all of my devices (including mobile). That way it's local but accessible from 'anywhere' (for me).
I wish HN had an easy way to save comments like Reddit, but this reply should do the trick :)