I'm with the consensus here - worth that little extra (only £100 - one of the cheaper options on the A5/S5!) The entrance lights (aka puddle lights) are great, and will keep your feet dry as you step in when it's really dark outside and it has been raining. Not included in the brochure list are rear footwell lights - and to my eye, they're blue.
I think the red illumination of the central dash is standard on all A5/S5s, but can't find a reference to it. I think it's something Audi have been doing on all their cars for a while. If you don't know what I'm talking about, then hold your hand near to the heater controls at night - your hand will be lit by a red light from near the sunglass holder which you just don't notice if you don't know it's there. Try covering this with one hand and then adjusting the heater with the other (when stationary, obviously!) - it's just not as easy because you can't see your hand! Weird huh?