I think how long will depend solely on how many times you flicked them on and off.

And also from what I have read, how long in between you usually fire the ballasts. Frequent firing is not good for bulb longevity.

It is pretty safe to say, whatever the case, that your bulbs are not as bright as they were when they were new. But how bright is subjective, so if you can still see safely at night, changing them may offer only minor improvement for the cost.

I think bulbs at the dealer run $150-200 for the set.

Prolumen H type bulbs will light up a little different then real HID D2S/D1S..Don't know why..
Here is mine lighting with 5500k.
http://www.xoutpost.com/717566-post10.html

Stock xenon (as any other xenon) has ballast already. Ballast is a separate unit providing high voltage to xenon bulb. You can change bulb normally (it has normal wire connectors) and don't need to worry about ballast.

thank you was worried if it burnsout

Well, the ballast can break down too, but it's not that common. If you suspect that this might be the case, you could test it with a bulb from the other side (if that's working ok).