Bit OTT IMO. Mine is a 2010 plate and looking at the guide price for trade in atm it looks like mine will have lost about £6k-£7k a year in the two and a half years I've had her which is about right for a large capacity sports car. One thing to be wary about is dealers that use the Glass guide. These guys are jokers, completely lowball prices in the guide, they are no where near market values. Parkers is far closer to prices seen on PH/Autotrader/eBay.
+1 on Parkers