oxidising lenses are common, you should get a headlight lens restoration kit such as of meguiars and if you are good at it you can have a go yourself, it involves sanding it down and then buffing and then finally protection and they look good as new, alternatively you can simply get hold of a compound like meguiars ultimate compound and try it ourself with a MF cloth there will be no harm and ovule clear them a little, meguiars plastx can help, basically you need a abrasive to get rid of the oxidation and then a polish to make it clear it again and then something to protect it form happening again, if not confident take it to a professional detailer he should be able to correct it, or watch videos on youtube on headlights lens restoration there are quite a lot just dont think toothpaste will work.
people may suggest you to get the headlight removed and clean it form inside but i advise against them, i haven't seen any before after pics that this method works even and removing the headlight involves dismantling the front bumper and cracking the seal of the headlights which they will not be able to get a good seal back anyways and moisture may later come.
you feel the high beam is not as good probably because the lens is oxidised and not letting light completely pass through. it has very specifically aimed headlights they dont scatter light all over the road like corolla but increase the illuminated distance quite a bit.
i would not suggest to install although it can be done, first youll need to find a 2 din plate which will be very difficult and it will look very odd plus wont work with the steering controls or display in the dials. if you already have command youll still need a hardware interface form uk to make it recognise the camera and its super expensive. and the camera is typically mounted in place of the license plate light it might be possible for it to set the light broken warning off, even if you get a feed form somewhere else care needs to be taken not to disturb the rear sam. its still doable but i wouldn't personally especially with the knowledge of our local electricians and audio installers and their armament of nitto tape.
proper way to do it is to get a command system form uk a original one can coast 1900 pounds upwards and a camera connection kit for it which can as far as i remember more than 500 pounds
you can refer to this website for audio related info on mercedes including what can and cannot be done while staying in the limits of OEM.
hopes this is of any help to you.