I know what you mean. I have been looking for the same thing. I have searched and tried all the plug-ins that seemed like it might do the protected viewing of posts by user groups.
After not doing what I needed it to do I found another blog software called Serendipity:
https://www.s9y.org/
It does do what I need through categories and user groups and its built in, also easy to install. But I have used WordPress for so long, I just wish I can continue. So I am on the fence right now.
Kay
