Thank you once again, Moviebob. Your line of thinking has coincided with my argument since the beginning of all of this whining about Avatar's non-originality, and even before the film was made. To be cliché regarding clichés: there is nothing new under the sun. To say that something is unoriginal is a completely irrelevant criticism - there is nothing original in the first place.
Why? That's easily explained. We have six billion people alive today, and about one hundred and six billion people who have lived on the Earth and died before us, with all of their stories to add to our own ones. In the face of odds that steep, to pretend that any story we write - even if it's in a made up language - is in any way "original" is the height of arrogance, so the only "originality" we perceive is 100% subjective.
This situation provides each of us, and ultimately humanity itself, with three major choices.
One, we follow the path of the aliens in your story. We split everything into broad, classified clichés, and everything becomes dust. We understand the trope, therefore the story has no meaning to us. We gain nothing "new" from it because we've "seen it before". As a result, the banality of the endless information sea eventually overrides our sense of enjoyment in said information, while our addiction to it continues to grow.
Two, we follow the path of the young man. We individualise everything, we understand meaning on the most subjective level, therefore enjoying our own experiences while decrying others', concluding on our superiority over beings potentially more objective and intelligent than ourselves. The result; a ceaseless wave of love for certain stories or genres that is so individual that we rarely have anything to relate to others about, or else polarise into groups so strongly defined by interest that they seem like new cultures... eventually leading to deeper conflicts and the destruction, once again, of enjoyment. This is something that has already happened on a small scale with the culture of the "fan", which has lead to conflicts like the console wars. These conflicts may seem small now, but if you multiply that subjectivity across the whole human race, imagine the consequences. "Harmful" would be an understatement.
The third option, a middle option of sorts, makes more sense to me. Why not classify the tropes and understand them objectively? But why not, in response to the tendency towards jadedness, nurture a sense of enjoyment when it comes to the commonality and archetypal nature of storytelling? The best of both worlds is easily achievable here - all it takes is to believe in meaning regardless of its commonality. After all, to be useful, meaning doesn't require originality - meaning is in meaning. Even if a hundred thousand people have walked our exact path previously, that doesn't make our own personal experience and variations in that path worthless. That doesn't make our own self-discovery meaningless. We see the dust, the base similarity of all stories, and we remember that though it is common, it is made from the stars of knowledge and wisdom. Enjoyment is thus maintained, and the addiction to information does not destroy the spice of life.
The aliens assume that for something to be meaningful, it must be interesting to them. The failure of logic there is obvious. The mistake in the young man's approach is less clear, but nevertheless present; he fails to realise the entertainment value of his story is degraded (for the aliens) by its commonality, even though that story retains meaning and useful conclusions about teenage love. Boredom and meaning are entirely different and separate concepts, and sadly neither alien nor human in this story understands the difference. Luckily, they need not connect at all times, if we dare to suspend belief. That is a challenge that the Information Age has presented to us, so I hope that we learn the lesson.