I think you should be linking to something about the Cost Theory of Value or Labor Theory of Value, rather than the Broken Window Fallacy.
Value is savings. Economy is savings.
Bitcoin is savings.
What does Bitcoin save? It saves the cost of transporting money across the globe. It saves the cost of inflationary theft inherent in fiat currencies.
Bitcoin's value derives from savings, not work. Work is the cost of using Bitcoin.
I'm altogether a BTC detractor, and I actually had the same initial reaction as you. But then I read more carefully and I realized that in the peculiar case of spam filtering, proving that you did useless work really *is* valuable. Presuming sending an email is valuable to you, and presuming having too many emails sent out is dis-valuable to the email service provider, being able to prove that you went through some trouble before sending out an email is enough to satisfy the email provider that you're not sending too many emails, is valuable to you.
This is an intriguing concept and it has a chance in turning the tide of my opinion. However, I think it's potentially flawed if taken in the full context of Bitcoin, as described in the first post. I'm still working it out. It may, in deed, still come down to the Cost Theory of Value in a sense, but not in an obvious way.