The only down side I see to a completely mobile system is the ease of theft. Every time you get out of the car you will have to hide everything or take a chance. The majority of auto theft is the grabbing of anything laying in plain site. They break a window and grab it and take off (15sec).
Anything that is added will be confronted with the problem of the low speaker quality and total lack of power to drive them. No matter what you add it will sound like scheiße.
I understand why many owners would not want to change the (outdated, underpowered, and inferior) Becker radio but updating the stereo does not require 'HACKING' of any kind.
Do not quickly dismiss the idea of upgrading to a modern sound system in our wonderful looking cars. Mercedes look great why not have them sound great too.
I wanted great a sounding sound system in my 68 coupe. I installed a new Kenwood head unit with 4-6.5" round speakers (2- front, 2- back) and 3-100 watt amps to drive everything. I removed the manufactures labels and painted the speaker covers to match the surrounding upholstery. All of the amps and wires are hidden away. The amps are behind the rear seat and under the rear deck. The wires run under the carpet and through existing holes in the trunk and engine fire wall.
There are many head units which fit easily into the preexisting hole on the dash.
I have bluetooth and a IPod connection (under the center consul). Everything is controlled through the head unit. I love the ease of use and the amazing sound quality.

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Britton McIntyre

68 280 SE coupe 'Hairball'
70 280 SL
71 280 SEL - RIP May 2010