Gehenna, you could always theme the event and cast accordingly. Ask all the potential performers for details of their acts... perhaps limit yourself to a musical period and then you could break it down from there?
Seems obvious and perhaps you already do it, but think about the flow of the evening, casting perhaps a firecracker of an act for opener, then a storyteller, then something more classical like a fandance/balloon pop, then finish with a skill based spectacular; like a singer/magician/fire performer or simply an odd prop! Or your headliner...
Just an idea
Have fun choosing
xx