Had basically the same feeling about Bling Ring. The company I work for sponsored the movie in Italy, so I felt some kind of interest in seeing it... and was utterly disappointed as well. I also expected there to be more character development and a "crash and burn" effect during the second half. Maybe that didn't happen because this is based on a true story. This is how it actually went down. And the most disturbing part was when the girl interviews at the end: she was the ringleader, but also the ultimate manipulator, and we only start to realize to what point she is evil in the last few seconds of the movie. It left me feeling empty.
Spring Breakers, on the other hand, is one I've been avoiding, not even watching when there's nothing else. Now, based on your comment... maybe I will watch it after all.