re: Fillmore. At the Opeth/Mastodon/Ghost show in May, they were handing out tickets to the Meshuggah/Baroness/Decapitated show a few weeks later. Both shows were face value $25, and both shows felt pretty full, but I guess they were having trouble selling tickets to the second show.
Also, at Meshuggah, someone in the audience mentioned that they were handing out tickets to the Danzig show a few weeks later, but I didn't see that myself.