I'd probably have to pay them to take my 2008 C class then it's worth more to me as a nice working vehicle, the problems come if it falls victim to an accident, I would never get what it would cost me to replace it with a similar low mileage (50K) car.
I'm in a similar position with my 2009 C class. While it won't be worth much I'm still only losing £100 a month or less in depreciation. My annual miles are too low to make the depreciation of a new car remotely sensible.
I have a spreadsheet that records the depreciation of every car I've ever owned and the average annual depreciation varies from 4.5% to 23 %. You can guess that the 23% car was bought new and kept for only 15 months. The 4.5% car was a 190e bought at 5 years old and kept for 21 years.
All of the cars I bought new depreciated more than 10% pa and all of the used cars depreciated less than 10% regardless of how long I kept them.
I have no problem with the PCP culture if it supplies the used market with cheap mint cars under 5 years old.