Nostr definitely has a spam problem. When I was gathering events for the Nostrum Search database, out of ~2.5 million events about 1.2 million were pure spam that had to be filtered out (mostly notes that didn't use any of canonical note "kinds"). I'm sure these issues will be tackled over time, but I agree that a pay-to-play LN solution is probably the best one. 

 Agreed. Although non-canonical kinds is just people experimenting with other uses of the protocol - irrelevant kinds don't influence the popular nostr clients focused on kind:1 posts. It might be a problem for relays, but then they could just ban useless kinds, so it's not a big issue. 

 Nostream supports whitelisting event kinds which should help