How would you feel if Warpcast replaced likes (the heart icon) with reddit / HN style upvote and added a downvote on every cast?

1 - strongly against this, would stop using the app
10 - hell yes, would greatly improve the experience

20, it's a good start, but doesn't go far enough. Ideally you'd be able to label content with any emoji you want, or at least a large set of standard emoji. Things like funny, shitty, brilliant, deceptive, etc. Similar to how Slack/Discord do it.
Then people can use their own client-side scoring to determine value.

https://github.com/farcasterxyz/protocol/discussions/89

Yup, exactly this sort of thing. This type of labeling will also enable you to build feeds based on labels, like if you want to prioritize things that people think are funny, or insightful, etc. For UX simplicity, Signal started only showing the top few labels. Might be a good approach if you're worried about UX bloat.