All of the following is IMHO. The value judgments here are my own and might not agree with those of the list-owner or its other members. No insult is intended to anyone. Here goes...
I recommend to reduce the amount of noise on the list, we adopt two simple rules, which can be automated so that no one need moderate the list.
The fist is a post per day per member maximum. This could be, say, three posts per day. By doing this, I think people who chime in on everything would choose what to respond to more wisely.
A potential problem with this is people who use multiple email addresses (like me, but not to this list:) would be able to circumvent this rule. I think list-owner intervention might stop this, though I would hope list members would obey the rule without such.
The second is a limit on the size of each post. This enforce trimming posts, so that members don't quote the whole post, but only the part they wish to respond to.
A problem with this is that combined with the post per day limit, the length of a member's daily contribution would be very limited. Even so, if someone has something lenthy to post, he or she could post a (temporary?) URL with the material or ask members to email him or her for copies of it.
I also suggest that if we do plan to adopt either or both of the above rules, we do so for a probationary period just to make sure that list quality and participation don't drop. I wouldn't want to make the list barren by enforcing such rules. A probationary period of one month might be good, then we can poll members to see if they think quality has gone up or down.
P.S.: Someone might have suggested the above before, but, if so, I do not mean to steal her or his ideas.