I don't think most relays look at pow, it's still a niche thing.
I also don't think it's very good for spam. Mostly it's good if you want to look at what people are willing to waste a lot of money or time on. What they think is important.
The best way to post notes with POW is with nostr:npub189j8y280mhezlp98ecmdzydn0r8970g4hpqpx3u9tcztynywfczqqr3tg8 (there is an option to pick how much POW in the settings) or with https://www.get-tao.app