I think that depends on what you're interested in. In my case, new content is the main thing. We pretty much knew what had happened during the reigns of the first couple of Targaryen kings, and I sort of liked the parts about Jaehaerys, but OTOH, he's supposed to be the super awesome uberking, so that stuff was less interesting. The reign of his immediate successor and the subsequent Dance of the Dragons were covered in previous material, so the part I enjoyed the most was the end, covering the regency of Aegon III, which had some really interesting politics. The wars I didn't find so interesting in these "historical" works, because the battles just seem to happen and you don't get much sense of why they do. The politics are better, I thought, and that's mostly the reign of Jaehaerys & the regency.