Well... since it is happening inside your head, you are really talking to yourself in a fancy way. Or at least, that is how I understand it, as I think all the astral stuff, connections to other people, and anything of the like is bogus.

It makes sense really, you are in a state that is almost completely ignoring the outside world, so this gives your brain so much more power to focus on mental things. Summoning great minds is expected to lead to better results than you naturally would have come up with, so your brain plays the part of those characters based on your knowledge of them.

(This may sound sorta creepy to some) I talk to myself (That is, a created second personality) allot throughout the day. It helps me remember tasks, recall information for classes, creating vivid memories I wish to recall later, and pass the time when bored with nothing to do. This "second" personality is like a whole different being in my head. I can have a conversation without putting noticeable conscious thought into it's responses, and yet, it often brings up points and issues to a discussion I would not have otherwise come up with (I have often ended a conversation thinking, "Wow, I never would have thought of that!" only to realize, this "other person" was in fact myself in the first place).

Now, if my brain can do that while I am awake while walking to class, why couldn't it do something like that on an extreme level when asleep where your brain is debatably as active as when you are awake, albeit without the distraction of physical input?

Anyway, these are my two cents on the subject. I certainly want to try things like this, and in fact I have a specific goal involving something like this I have been aiming to try with my next lucid (Sadly, lucidity is avoiding me). Something specific I also want to try is to change certain personal traits and desires by altering relating objects in the dream state.