The thing with the nest scene is that even though it has been stated outside the film that Brett and Dallas were morphing into Alien eggs, just by watching the film, is that completely obvious? Whose to say that they aren't just being cocooned for eventual insemination by a queen. Maybe the soldier aliens originally weren't especially intelligent (although "Aliens" disproves that) and they were just drones doing work for a queen that will never arrive. Who knows really, but it is fun to hear all the interpretations of the Alien and their life cycles