I watched some of the commentarys last night after failing miserably to sync my ipod touch with my ps3 to get the live extras. I was excited to see what the trio had to say about the first head chamber scene. One thing that stuck out for me was that Ridley mentioned there would be no "Spielberg wonder moments" in this film, as they are all scientists. I presume by this he means the hands on hips, open mouthed, gawping look with dramatic score that Spielberg often puts in his films.
I personally thought this was a shame, as the giant head reveal should surely have been one of the best "wonder moments" in the film.
Secondly, I was also slightly disappointed that they didn't have a lot to say about the head, the altar or the alien murial. By not a lot, I mean nothing. Ridley at least talked about the technical aspects of filming that scene, but Damon just waffled on about story arcs while Spaihts probably was sat in the back of the room with his head in his hands.
I suppose that for now, this can only confirm that these elements are "for show", and their relevence at the moment, if any, will hopefully be explored in any sequels. Polar bear all over again.
Rich