I always liked having karma around as a personal metric, but I never actually looked at anyone else's or went farming for it. So I think it should be added but not made a determining factor by default. If someone wants to look at someone else's karma as an evaluation, that's their choice.
Probably more important than Karma, Lemmy needs flair or tagging for posts to help with categorization and searching.
In addition to that, Lemmy (and Mastodon) eventually needs algorithmic choice. This is one place where the Fediverse falls short compared to BlueSky. A chronological feed of everything is a good place to start but let me decide what I want to view and how I want to view it. For example, if I am person that cares about karma, let me weight that so people with higher karma show up higher on my feed.
Atari 2600 followed by NES