In an attempt to win a Good Net Citizen award I have been trying to register my Mailhosts. This has been quite difficult and I want to see if I understand the benefits to 1. myself 2. anyone else.

My sense is that if I succeed in configuring Mailhosts correctly -

a. I will be able to report spam in a way that reduces the risk of false attribution of spamming to entities that are really just email service providers, due to use of forged headers by real spammers
b. as more SpamCop reporters get Mailhosts configured, the reliability of spam reports (w.r.t. this false attribution issue) will increase
c. this in turn opens up the possibility of making Mailhost configuration mandatory
d. at some point in the near future, header forging will be widespread and this could make SpamCop useless unless most/all reporters are Mailhost configured. Correctly configured!
e. even though there are only a small number of SpamCop reporters and an even smaller number who are Mailhost configured, they are hopefully enough to make a difference against spam.

(Or maybe reporters are irrelevant, counterproductive even, and the system should rely solely on spamtraps?)

I really did need to think about that, as it was pretty onerous to get the configuration done. I hope it's been worth the effort?

You are only reducing the risk of reporting your own mail handlers incorrectly. The problem in a nutshell is that with quick reporting, there is no check before reports are sent iand in many cases, people were reporting their own ISP and getting them listed.

Is that all? So am I not (also) helping to make SpamCop resistant to an imminent threat from well-forged headers? Helping to ensure SpamCop does not become overwhelmed by false attributions of spam to ISP and email service providers?

...Correct, that is all MailHosts configuration does. Efforts to ensure that SpamCop does not fall prey to well-forged headers and thus falsely attributing spam to the wrong ISP/MSP is why there are SpamCop admins and one or more programmer/analysts.

stated in another light .. it was "well-forged headers" that led to the creation of the MailHost Configuraton of a Reporting Account situation.