No, I use browser bookmarks which eventually get sorted and migrate to a kanban or a bookmarks bar. It’s unlikely that I revisit something outside of this path.
Yes, that's basically the only thing I use upvotes for. "Favorites" are useless IMO, since you can't access the "favorite" link from the front page.
I upvote too many comments for that to be useful.
I never thought about it this way, but it is nice and interesting browsing my upvote history. So probably in a subconscious way - yes.