To explore new parts of the site, simply page through /s/all/new. But if subs aren't working for you, maybe you want tags instead.

Viewing posts based on tag is a good idea. It's been proposed before. Tags versus containers is a long debate on things like bookmarks. Though I haven't seen a reddit-like site that's implemented it yet, so I don't know exactly what it would look like.

You could #tag or whatever all your own posts, or in a sub of your own, and try to get it to catch on.

Making it easier to find posts based on tags might increase participation. Duplicate posts, for me, would not. I've seen that before and it's tiresome.

Edit: Actually, I can think of some sites that use tags, but their interfaces are tuned for microblogging rather than link aggrogation. Minds and Gurlic both use tags and timelines, but I can't tell if I hate their tags or just their Facebook/Twitter style. Oh well.