There pretty much seems to be one global blog per space.

I would like blog posts to be more like pages in that they have parents / children, and thus we can filter blog posts based on position in the hierarchy.

(You can filter by date / time, but there isn't a great way to set up a team or department blog. Perhaps I did the wrong thing in setting up pretty much everything in one space, but based on informal user testing we found that to be much better-- the partitioned
namespaces were harder for less technical users to conceptualize)