Easterhay said:

The reason, though, that the prequels look so differently to the originals is that we're seeing The Republic in its prime

I disagree. The biggest source of the visual difference between the prequels and the originals is the over-use of blue screen and computer generated imagery in the prequels. George Lucas and Francis Ford Coppola talk about the idea of a "used future" in the special features to THX-1138. Just because the Republic was at its height does not mean that everything would have looked the way it did in the prequels: there should still be more of a used feel in the Old Republic, which, we are led to believe, had been around for quite a while.