"a granite shaft found between the pyramid of Khafre — also known by its Greek name of Chephren — Giza's second-largest tomb of a pharaoh, and the Sphinx. "
I think it's also amazing where they were found. That means there is a shaft between the pyramid and the sphynx -- so why did they make it?
There may be other shafts.
Some have been guessing, that there may be underground chambers underneath the Sphynx -- this find makes those guesses more realistic.
I think so. I believe it's an archive of some sort. Building a statue like that just for the fun of it seems odd. I'll bet there's a lot of stuff yet to be discovered there. It should be very interesting, because it's not a typical tomb.
Campbell's Tomb, basically a shaft dug in the plain behind the Sphinx, might be construed as some part of some ancient system of tunnels, but very little was found in it when it was cleared by Vyse; it may have been built during the 4th Dynasty, but was reused at some much later date. The 18th dynasty got all squishy about Giza, at the latest Thutmose IV, who had the Dream Stele erected between the paws of the Sphinx.
Campbell's Tomb
http://www.touregypt.net/petrie/c15.html#104
Thutmose IV's Dream Stele
http://www.touregypt.net/featurestories/tuthmosis4.htm