As I have posted elsewhere on here it is a very worthwhile upgrade. I upgraded a basic $15 auto shop cheapy to 35W HID. BTW a 35W HID throws out 3 times as much light (3300+ lumens) as a 100W Halogen globe. If that is not going to dazzle an animal, I don't know what will.
I bought a kit off ebay for $69 which came with 2 sets of 35W globes and Ballasts. I used one and the other is in the cupboard as a spare. There are pics of this spotty on 2 or 3 other threads here already.
Just to demonstrate how much light HID's produce. I have upgraded the secondary main beams and the Hella Rally 4000 FF Compact driving lights on my BA Falcon. They are so strong now that a few weeks ago, while driving on the Vasse Highway between Nannup and Busselton in WA, I lit up a road sign from a GPS measured 3.5km down the road. The outboard headlight units run +50 H4 globes. So at full power on high beam, I have two 60 watt halogen and four 35 watt HID globes burning. Did I mention I'm driving across the Nullabor in October for a wedding in Dubbo??
Oh and one last thing. The HID's produce perhaps a quarter of the heat of the halogen globes.