Yeah it will start getting dull again after a few weeks. When i take my car to the carwash at night i notice that it immediately reacts and oxidizes once you use the high pressure spray. Its very noticeable as it only happens to the drivers side headlights.

I use autoglym paint renovator to polish the oxidation off and use NXT2.0 wax to protect it, which is good for 3 months or so. I use NXT wax for my laptop too!