"If you walked up to the average person on the street in 1977 and asked them to think of an alien, what is the first thing that would come to mind: would it be 'a monster from outer space' or 'a foreigner in a sovereign land without proper visas'?"
I was born in 1964, hence 13 in 1977. To me and all my contemporaries the word "alien" definitely meant "space alien". I distinctly remember being rather proud of myself for even knowing that the word also had an older meaning of "foreigner".
On the other hand, my Penguin English Dictionary first published in August 1965 defines the noun alien thus: "foreigner, esp one living in one's own country and not naturalized." Not a tentacle in sight.
Added later: I was 15 when the film "Alien" came out. It was X-rated so I couldn't go and see it, but I do recall a hearing a graphic second-hand description of the "chestburster" scene from a friend whose older brother had seen the film. I do not remember ever giving a thought to the title.
(Sorry for the late edit. That last bit was something I had to get off my chest.)