Jim I reckon £6250 is about right mate, unfortunately the ICE is not worth a lot to most people, most other good points about your car are just service items i.e. discs and pads, nice to know they are good quality but again add little value...
If you can bring yourself to do it I would put the standard Bose back in and sell the ICE seperately to someone as an upgrade, I wouldn't expect it to affect anyone interested in the car or the price either way personally....