Hey, Ralph.
As you said, all encounters were non-physical, with beings "alien" to you. Of course we have now plenty of cultural stereotypes to represent such "alienness" nowadays, including the greys. On the other hand, perhaps they are what they seem. How could I know?
Who knows what kind of consciousnesses exist out there or where even you or I came from "originally"? There are many people who believe that beings from other reality systems incarnate here, and maybe you remind yourself of a past life.
The interesting thing is that these dreams remind you of something - yes, there is something more than your everyday reality. Like the flying craft. I remember one dream where I saw an UFO and it was so real, it reacted to me, I danced in the streets out of the sheer joy of having seen such an extraordinary thing! (what a disappointment to wake up and realise that it was a dream - but remembering it is wonderful nevertheless)
The fact that sometimes they teach you something and that you communicate with telepathy with these beings that these are indeed non-physical beings. There is so much to learn from "the other side", and maybe this is your reminder to always remember and maybe explore that.
I know I have certain kinds of dreams where I know they are important, too. And this may be your way to represent something vital to yourself.
Be well