Oh, I think spirits DO come to visit us in dreams. whether it is just to say HI, or to help solve a problem, or just to let us know that we are loved and they are always with us. I also believe we astrally travel to the Other Side and visit with friends and family.
Father's day, year before last, I dreamed of my father (he died when i was 8 and even 32 yrs later i still miss him!!)
He was fishing off the quaint little bridge. I called to him "happy father's day daddy!" and he just smiled and waved to me.
I am sure there are others that i just don't remember.
I also dream frequently of my mom's best friend who was like another mother to me. I don't think every dream is a visit , but i believe they happen!