I'm annoyed at the bit about people polishing up their social media posts being mere useless signalling-- a net with more intelligent, wittier posts is presumably actually giving pleasure and possibly usefulness.
Occasionally signalling leads to the production of long-term value. Sometimes rich people showing off produces art that people continue to enjoy. I don't have a feeling for when a signalling competition is about totally useless things and when it's about soemwhat useful things, especially those with enduring value.
I think only in a few cases do the signaling externalities consume 100% of the benefits of some activity. (Really I don't think it's true even for the swiss watch example.)
Polishing up social media posts can have both useful components, since better posts are better for the reader, and a zero-sum component. In this case the positive effects are also external to the post-writer, so I agree that it's actually unclear whether you end up with too much or too little polish.