I've been writing about Private blogs, and the ability to limit even the readership of the blog, for some time.
What if you want to have some posts accessible by a few people, and others by everybody? Or maybe you would like some of your administrators to have the ability to edit only a portion of your blog.
A content management system might provide security settings on a post by post basis, but Blogger is a blogging platform.
With Blogger blogs, you can set security only on a blog by blog basis.
The ability to set security on a post by post basis was one of the many issues discussed in the Appspot forum, in early 2009. It did not receive a large amount of votes.
But nobody said that you have to have everything in one blog. Having different security levels for different blog sections is similar to having different template objects for different blog posts.
Setup a second blog, as like the current one as you wish - but with different security settings, or maybe as a private blog. Then combine the two blogs for your readers.
To your readers, you'll have 1 blog. To you, you can have many blogs. And your blog members will have only the access that you want each one to have.