I don't tend to get to hung up on what the 'Trade' says and to me the Glass's guide is so far out of touch, especially with sought after specialist models. Yes your run of the mill rep mobiles and family wagons will rarely achieve top book value, but the more sought after variants are fair game.
The last 5+ cars I have sold have been well over the 'Trade' guide proving to me that people will pay decent money if the car is the right one. If someone wants a well specced looked after ED30 then why shouldn't it achieve 12-15k depending on the age/mileage/condition?
In my mind 12k for the car in question is a steal, a lot of very good hot hatch for the money.