It’s probably useful to mute/block non-spam by nip05.

But for spam or attacks its a losing game, attackers can change nip05 very fast, and when you receive a post you have to first get the kind-0 profile, then check the domain, those are “expensive” checks and with spam you want to do as little work as possible.

With WoT you can discard a post almost immediately without even checking the signature. Proof of Work on the pubkey is also a very fast check but this has other problems. 

So far I have not found other solutions that don’t require the defender to do more work than the attacker but thats the type of solutions I prefer to implement.