Ian, having been in both my brothers S4 with OE Xenons, and our A4 with retrofitted halogen projectors i can say that while yes the HID's are brighter, they dont actually illuminate any more of the road.
How much they illuminate is governed by the beam cutoff on the projector, which is the same on both setups.
I mean sure the HID's were brighter, but only to the beam cutoff, and on a dark windy country road, it can feel as though that cutoff it a bit too close, however i cant say i'd call the halogens dangerous, they're just not as bright. On both cars you can clearly see the line of the beam cutoff.
If you think they are dangerous, then i suggest you first check the alignment of the lamps before going any further. The fact the foglights helped atall does suggest there is a problem. The foglights only really act as infill at the corners in my experience. They improve the lighting at the sides of the road, but dont make any odds in the middle where the main projector is shining.
Theres a guide floating around that shows you how to set the alignment of the projectors in relation to each other and the road, i'd give that a spin.