I think you need to re-examine your belief that "spectating is fairly passive on the whole". Your spectator needs to be involved in the effect, not just be a passive observer. If he or she is involved, then that will afford you opportunities to display your ability to be funny. Additionally, you can script effects that are comedic in nature. Take a look at Wayne Dobson's ECHO as an example. It is a very magical effect and the way he has designed it is also has the potential to be extremely funny.