The evidence is that, if it became clear that a serious effort was developing to deploy such filters, the spammers would start sending conforming messages more rapidly than the filters could actually be spun up. Would this inconvenience them, or the authors of spam tools? Yes, but almost certainly not very much or for very long. It would, perversely, actually help the businesses of the spam tool builders: "get your new, updated, standards-conforming bulk mailer here and get past the new 2821-conformance-testing filters".
I agree and am coming to the conclusion that there won't be any technical solution to SPAM. The SPAMers will adapt to all technical hurdles that are put in place. The solution needs to be at the policy and/or legal level.
I also agree with Tony Hain that the current remedies may be doing more long term harm to the Internet than the problem.
Bob