I think pow is better for discovery than spam prevention. People might be ok with paying for pow for an occasional announcement you want people to pay attention to, but mobile users will not want to drain their batteries to post likes.
nostr:npub1xtscya34g58tk0z605fvr788k263gsu6cy9x0mhnm87echrgufzsevkk5s, could I try and bring https://github.com/damus-io/damus/pull/172/ up to date (probably as a new pull request) so that Damus sends messages with PoW automatically? I know you said that you think Lightning is a better filter, but every single person sending notes on Nostr can calculate PoW since they obviously already have a computer whereas the same is not true for Lightning. If Damus leads the charge on this and if we can get nostr:npub1gcxzte5zlkncx26j68ez60fzkvtkm9e0vrwdcvsjakxf9mu9qewqlfnj5z on board we could make PoW default on notes which could almost completely solve the spam problem.
Discussion
Even if it only takes a few seconds? It’s not like you’d need to run your CPU for hours to send a note.