This is not exactly an answer to the question, but it is the simplest thing I know to help students appreciate complex numbers. (I got the idea somewhere else, but I forgot exactly where.)
It's something even much younger students can appreciate. Recall that on the real number line, multiplying a number by -1 "flips" it, that is, it rotates the point 180 degrees about the origin. Introduce the imaginary number line (perpendicular to the real number line) then introduce multiplication by i as a rotation by 90 degrees. I think most students would appreciate operations on complex numbers if they visualize them as movements of points on the complex plane.
