Do you have experience of aftermarket HID conversion kits, and do they make night time driving better ( I'm loathe to say safer as you'll probably bang on about incorrect filament geometry dazzling on-coming drivers
If the geometry were the same as the homologated lamp, then presumably the advantage to HIDs will be a brighter illuminated area - as opposed to a greater lit range?
I've never actually driven on a set of aftermarket conversion kits. I have driven on OEM lamps designed for HID and I do have to say that I think they are excellent if designed properly. Sometimes they can be very tiring to drive on if travelling for a while as they actually become quite straining on the eye.
This problem occurs because you get a very sharp cutoff (necessary to obtain the gradient required to get down to the legal glare levels from the high intensity in the beam). What happens is that your brain will want to try and see through the cutoff (it doesn't like the light/no light effect on the road) and you will find that you do start to strain your eyes trying to see whats in that dark zone. Properly designed HID lamps will try and soften the cutoff and make it more blurry to make it easier on the brain and hence the eyes. It is one of the big criticisms that we encounter when designing HID lamps and alot of work goes into getting the cutoff right.
In some ways Halogen lamps can be better in this respect as you can have a much softer cutoff due to the lower intensities in the beam, and also your eye doesn't shutter down quite so much and you can actually see more. Much like the fact that you can actually see in a darkend room once your eyes adjust.
That said, HID burners do produce 4x the light of a halogen bulb and this will give much improved illumination of the road infront of you and vastly more illumination to the sides of the distribution (infact that is the only way we can keep the illumination to the legal levels is by 'wasting' the light out to the sides). This will give you the 'sense' of much better lighting, and hence an added sense of security, however, whether you will actually be able to see any further down the road is not a given. You will get a better view of pedestrians, dogs, and anything else that is about to jump out from the bundu at you.
Given that no conversion kit will be legal, the decision is yours. I personally just make sure my lamps are aimed correctly, kept clean, and have the best quality bulbs possible, and whilst I do occasionally find myself wanting a bit more light, in general I find the standard setup acceptable for the job. So, if you think that a brighter illuminated area is an advantage then have a go, all legal issues aside, personally I prefer to be able to see the required distance without my eyes becoming fatigued.
Sorry for the wordy reply, I can get a bit carried away trying to give as much info as possible