First let me say that I think JC and Brad are doing a great job moderating the lists, and I /greatly/ appreciate their help with this!
Second, I think there's one more use case that might work well for general help lists like mailman-users (but not mailman-developers). There should be a way for non-members to "self-moderate", essentially using a technique similar to subscription confirmations. If you were a non-member poster who replied to the confirmation, your message would go through. Non-confirmed posts would be automatically discarded or bounced after a certain amount of time.
Come to think of it, a list like mailman-developers could use a variant similar to the confirm-and-approve for subscriptions. Admins would only see confirmed messages in their queue. At that point, most spam should be deleted and the moderator only as to decide whether the message is on-topic or not (something that will always be a judgment call).
-Barry