Install pecl/inclued

extension=inclued.so
inclued.enabled=1
inclued.dumpdir=/tmp

Generate graph

~> php ~/pecl/inclued/gengraph.php -i /tmp/inclued.27843.1
Written inclued.out.dot...
~> dot -Tpng -o wp_inclued1.png inclued.out.dot

Not bad, no redundant include_once/require_once (would show as dotted lines). Still too many levels for my liking though. If you are reading this on the Web, right-click and load the image in a separate tab to see it better.