its a shame when a modded car such as this has to be put back to standard.... but if you are trading the car in or selling it at a standard (or below book) price, then it just makes financial sense to remove all mods, sell them on seperately (which would bring in quite a bit with decent mods), and then put the cash towards new mods for your new motor.
i know when i come to sell my CLK Cabrio in a year's time for the S Class LWB CDI i want, then i'll be trying to sell it with mods and then if no takers or silly price, it will be stripped back to all the standard stuff that was on it when i got it.