I had HID on my Infiniti (they were called Xenon headlamps in those days), my brother has them on his '05 BMW 330 and his even turn with steering input. They are not worth investing the time, much less the money. My experience was the only time they add any value was when reading street signs at night in the rain. In fact, the sharp contrast between the bright edge of the lit area and dark of the totally not lit area can sometimes surprise you if an animal suddenly pops into view. With Halogens, that line is less crisp and you see a shadow of the animal first. I can't comment on if the aiming of a xenon would be higher than that of a halogen, but you certainly could adjust it at the risk of annoying other drivers.

Of course, the cool factor is there, so if that's the reason and 5 pairs of Oakleys or Ray Bans are not as cool, go for it! It's your car, it should look how you want it, but don't kid yourself that there is a reason for it beyond tinkering with the car or going for the blue/purple look.

A society grows great when one plants trees in whose shade he will never sit.
- (I Forget. Anyone who knows, remind me)