Let’s be honest: Despite many popular attractions onstage, these amphitheaters are as temporary as Katy Perry’s hairdo. Mystic Lake Casino in Prior Lake has once again put up an outdoor stage and chairs, making room for 8,000 people to see Lionel Richie, Santana and Blink-182. This summer, Treasure Island Casino in Red Wing assembled an ambitious schedule with nine outdoor concerts, featuring the likes of Willie Nelson, Adam Sandler and Journey, which drew 14,000 people on July 1. Or do we? We have two major facsimiles and whether they’re reasonable or not, that’s debatable. Hey, Twin Cities, welcome to the Big Leagues of Concerts.