Dont try to polish the inside of the lens. It is very soft.
Some gentle soap and buffing gently with a microfibre cloth does the trick on the inside of the lens.
Same goes for the reflectors, the chrome is very very thin and will rub off even with too much pressure, even with a micrfibre cloth. You have to be very gentle with it.

Most of the cloudiness is damage on the outside. Unless you've had a leaky headlight, or a lot of dust get inside, there's probably not much point in opening it up.

Cool, thanks for the tips mate . Was only going to do a quick once over with some plastic polish just to clean the surfaces really, but it's good to know what to do and what not to do when the time comes anyways.

Cheers.