My thoughts on friending: This is how I gather together the people I'd like to read. It's like subscribing. So (in my opinion) anyone should be able to friend anyone else they find interesting. Asking permission to friend strikes me as bizarre. You don't infringe on the person's private posts unless they friend you back, which is their choice.
Of course it might be polite to introduce oneself and say, "Hi, I think you're interesting and am going to read you from now on." Just to meet people. Normal people might act like that.
I don't yet have a coherent policy for who I friend back or how I think about that.