What I've wanted for a while is some way for to give guidance to Facebook about which friend clusters are likely to enjoy what things. This way contra dance posts are more likely to go to contra dancers, EA posts to EAs, etc, but everything is still public.

I don't have a solution to the general case, but in the case of kid stuff the difference in what people want to see is really strong, so it's worth figuring something out even if it's not ideal. What we've been doing is keeping a group for pictures etc of our kids. Several other parents we're friends with do this too. It works pretty well, but the main failing is people who would like to see kid stuff but don't know about the group. So, in addition to describing the problem and our awkward solution, this post also serves as notification that this group exists.