With regards to the point of the prequels, while I've seen but a short bit of them, and recognize that they aren't exactly high art, I do challenge the notion that all they offer is history that was already known. Part of the idea was of the degeneration of a republic into an empire complete with powerful renegade factions, and of course of the psychological development of individuals in that system, the future Darth Vader most particularly. I know there's more to it than that, and it probably wasn't well done, but it certainly helps to establish the decay, both physical and political, that was seen in the original trilogy.
