You can't define a standard for illegal behavior that encompasses most of what the medium is designed to do.
Trying to measure this by word count is completely socially inept. It's not about word count, it's about the fact that they don't actually give a crap about me or my goals: they're just trying to sell me their product. I don't care if 100% of the words in the message are hand-crafted to appeal to me: if they're just trying to convert me as a revenue stream instead of actually trying to address me as a person, I don't want to hear from them, even once.
Also, your example falls under the Compliant class of emails under the act.
Edit: (since I can't reply to a poster from whom I received a down vote)
I agree, the act is too narrow in my opinion. I don't equate clicking "spam" with compliance with the law. I was simply stating that the parent post's "slippery slope" assertion wasn't accurate in this case.
Compliance with law is not sufficient to stop me (and many other people) from just reporting as spam.
Laws always have some room for interpretation.
Laws have room for interpretation, but again, they can't be written in a way that includes legitimate uses as illegal behavior, or the law is worse than useless. Define a rule that says (essentially) "you know spam when you see it", and you end up where pornography is: email marketing will be legal, with random, ineffective, arbitrary restrictions that make business within the domain unseemly and difficult.
Said another way: criminalize unsolicited email and only criminals will send emails.
There is perhaps a distinction that could go really far, though: unsolicited email from and on behalf of an individual, not a company, legal entity, or service provider, is 1000× more likely to be acceptable than the latter!
What? That's wrong. UBE has always been hated, ever since the Project Gutenberg guy tried to email the US constitution to everyone who had an email address.
You can't win this game.