The projector headlights are much better at focusing the light ahead of you rather than just blasting it out forward with your conventional lights.
The bulb is inside a focused lens therefore if you do upgrade to HID bulbs it will be just the same. I've got the LTZ and will be adding HID's soon.
For the extra money on the LTZ you also get all kinds of other goodies like the power lift gate, leather, chrome package, ambient lighting, memory seats, ect... over the life of the vehicle or your payment term it's a small premium but well worth it. I think most people only opt out of the LTZ because they prefer cloth over leather.