Hmm, 80% is a lot.
Could one get the same effect with a lightbox plane behind the 'coils', keeping in mind that the coils would have to be much thinner, get progressively thicker in the front and the amount would have to be much, much more? You'd need to arrange groups of these thin coils to get the 'banding' effect. You wouldn't need the diffusion effect and it won't have to render shadows. Though perhaps this would lose the 3D effect too much and I don't know if the added geometry doesn't simply slow the render down again.
On second thought, I have no idea how one could do it differently. Seems to me like your method is the one that takes the least effort yet gives a great visually interesting image. That's why I called it genius, even if it does take a while to render.