The HIDs in the stock housings are bright enough to overcome the problems of the OEM reflector and lens design, but it's still not ideal. If you're willing to spend the mony, I would really recommend getting a set of the TYC housings and dropping either a bi-xenon projector in from a BMW/Audi or a single low beam projector into the single piece housings.
Putting a complete projector into an existing housing will require a slight bit of custom fabrication, but it'll give you the best results. If you don't want to deal with cutting a bit of plastic, you can always get the plug in kit from that link and drop it into a pair of H4 housings (not stock) and still have close to the same thing- but the disadvantages are that you're still relying on the reflector instead of the OEM projector, and bulbs will be harder to find if/when they burn out because HID kits aren't exactly legal in the US.
TYC H4 housing (no corner): $100
High/low H4 HID kit: $540
TYC one piece: $200-220
Low H1 HID kit: $400
TYC H4 housing (no corner): $100
Bi-xenon BMW or Audi projectors off eBay: $400
Your choice man- all of these will give really great results.
I have a friend that had just a low beam H4 HID kit in his stock EG housings, and the light output was still pretty good. He said that there was quite a bit of scatter from the fluted lens on the front of the OEM housing, but with the headlight adjusted ALL the way down he was able to not have people ever flash their lights at him. He still had quite a bit of usable light. I'd stay the hell away from the stock housings though.