Lemmynsfw solved this by disabling downvotes. I don't think memes were a problem there.

An alternative is strong moderation to keep off-topic comments and posts out.

Isn't the situation in gonewild a clear sign it'd be wise to set up two separate communities? gonewildgals and gonewildguys or something? If a community is "too broad", niche content will always lose out. The answer is usually setting up a new community specific to that niche.

Fighting low-effort posts and memes either means setting up a meme community, more moderation on the posts or both.

I just block meme-posters and meme communities and my Fediverse stays interesting as a result. No need to convince/wait for the world to change when I can conveniently block the slop myself, it's one of the most appreciated features of PieFed/Lemmy imho.
Recall that whole db0 defederation of feddit.org? Was not a problem for me at all because I had already blocked the instance long before the whole thing kicked off simply because I didn't speak German and didn't want my feed full of German posts I couldn't understand anyway.

I don't think any form of rework on voting system would work; everyone has their own criteria, and it won't always make sense to everyone. Preventing upvotes/downvotes would just be a hindrance, and it also opens up a way to manipulate votes to however mods want.

One solution would be to have a community dedicated to discussions so that they have a chance to appear at the top.