The L is TOTALLY worth the 2x price jump. The IS alone is incredible. 4 stops! I use this lens now for wedding photography ALL the time. In fact. If my all time favorite wedding portrait lens now! Highly recommend the L.
What is it about the 100/2.8L IS that makes you prefer it (on weddings) to the 70-200/2.8L IS II? Is it the less intimidating size or macro capability? IQ seems very comparable at 100mm, with the macro having a tad nicer bokeh. The 70-200, on the other hand, is much more versatile for portraits, so I would have thought you'd prefer that.