As someone who has the factory HID's, I can tell you that it is indeed a pretty big difference. The OEM ones are white (not blue). They are only blueish for the 2 seconds that they are warming up. Also, the factory HID's have a little switch inside on the dash (next to the dash light dimmer) that allows you to adjust them up and down. Not sure how many people actually use this as mine hasn't moved since I bought it but it does give you some semblance of control. They are obviously motorized since you can see them move up and down with that switch which makes me wonder why Subaru couldn't make the Limited a couple dollars more expensive and just put auto-leveling in there.
That being said, while I am not a fan of Fake-I-D's, it's not AS bad in a halogen projector as it is with those morons with 96 Ford Explorers that put HID kits into non-projector headlights. Talk about glare! There's more light in the sky than on the road with those things! Regardless, using HID's in a halogen housing is wrong. It's illegal, and it pisses people off. I can't stand people taking pictures from inside their car, looking ahead and saying there is no glare. Try being the person coming towards you on a pitch black winding roadway. That's where there is glare.
I design roadway lighting systems as part of my job. We have to constantly take into account Illuminance, Luminance, Veiling Luminance, STV Ratio, etc. I won't bore you with the details but I will say that there is a lot more too it than what you see looking out of your front windshield. ..