I think, it'd be totally worth it. Already now, while #Nostr has a tiny user base, there are already issues with scammers, spammers, shit posters etc.

Filtering by NIP-5 would significantly reduce those issues, because then they'd have to waste their own domains, which will be blocked rather quickly & public NIP-5 things probably use Captchas anyway, so you don't want to batch create hundreds of such addresses with Captchas in your way.

Then, it'd be additionally nice to generally filter by multi-verified accounts, which have GitHub, etc. verifications accomplished. Such measures would quickly weed out much of the spam/scam & there would still be nothing stopping you from adding a weird account, without any verification whatsoever, as long as you do it voluntarily, rather than being spammed to hell by it on your feed.