That is lovely.

An idea which will change gameplay dynamic;

Have clicking the left mouse button create an invisible object at the x, y where you clicked and a different invisible object which does the same for the right mouse button and have the pianist and the singer shoot a musical note towards each respective object. When the note contacts the objects have them explode music outward. Make the helicopters move from the top of the screen towards the pianist or the singer and you have a Missile Command clone. For extra challenge add in more "bases", have an orchestra or dinosaurs or something. Maybe have a musical inspiration/ammo meter to add a sense of strategy and "waves" of helicopters.