But I tend to agree with you: We might have to face the fact that we have to improve the SPAM filter on our end and open the list. As a first step we could install greylisting and have a bunch of moderators to see how that goes.
@Jacob: How do you feel about that ?
That sounds like a good idea, as long as it is a temporary (< 1year) solution. Certainly better than changing the list, and then changing it again.