I've got factory HIDs on my CL9, I cant live without them. Its well worth doing the HID kit.

As for fog lights, I've done mine using a cheaper eBay kit and it was a great move. It now matches the colour of the HID headlights. Looks great. I dont use my fog lights as much as others, but for those foggy mornings, its very cool. I also like symmetry so, I had to get HID fogs and upgrade my main HIDs to the 6000k

Oh yeah - stick with 4300k or 6000k max. Anything above 6000k looks cheap in my opinion (like a dodgy aftermarket job)