The last Mastodon tour was intentionally booked at small venues, and they should only be drawing bigger crowds last time because of the people that missed out last time and the new album.
The last Dethklok tour was the first tour to hit pretty much everywhere, not just 10-15 college campuses. It sounded like it was just as much for fans of the show as it was for fans of the music. Now that the awe factor of a Dethklok show is gone and everyone knows there won't be any deaths during the performance, it should only draw as many or less than the last time.
8/20 High on Fire 4free
11/16 Judas Priest