PoW as costly signal is no different from... errr... "a costly signal" from the signal interpreters point of view. If I receive a message that someone has burnt $10 on PoW to send it to me I'm more likely to read it than one that was free to send. But if they burnt $10 on extra transaction fees or sent $10 to a known charity the signal is identical from my point of view. They have $10 worth of incentive to want me to pay attention. It only becomes different when the $10 goes to the reader as an incentive to read it, then you get fake attention because the choice to read is economically motivated rather that motivation being piqued interest in why someone was willing to spend high for my attention. PoW works in the context of Bitcoin... In the BoostPoW context it's just a fetish that diverts from Bitcoin's security unnecessarilly.