Honestly, I think the band are just flat-out better song writers than they used to be. Which isn't meant to knock any of the older material, because that stuff is eternally classic. But everyone in the band has sort of "grown up" and all become better song writers. With the possible exception of Dave. But I only say that because Dave writes less and less over the years, not as a reflection of the quality of his material.
Songs like Starblind, Wild Wind, Empire, Senjutsu, Isle of Avalon, Paschendale (just off the top of my head) are songs the band never could have written in the 80s. At least, I don't think so. There's a certain straight-forwardness of their earlier material that the band abandons now and gets more adventurous, and I love to see them do that.