Castes have such an affect on the way we read the Ramayana. The Ramayana definitely plays in favor of the upper castes. I think this epic would also be the writing that someone would use to argue the benefits of the castes. Even though Rama is banished from his kingdom and doesn't actually get to ascend the throne, he is still very kingly in the way he acts and the way he is portrayed. One could argue that even when life doesn't go the way it is supposed to it, we all have a dharma to follow according to our caste. This also affects the way we view other characters throughout the book, and we begin to think that the evil ones will have bad karma in the next life. Therefore, they will be cursed to a lower caste and that is why they are important.
However, I don't think this would be a good thing. I think having the castes creates so many issues. I think the Ramayana plays into to ideas of the need for the caste system.