New model has a few interesting improvements, new navigation and better brakes are the best bits to me. Personally not a fan of a new wheels. Also if you are going manual then the manual box in the revised model has longer ratios and a better feel apparently. I've done 100k now in an early manual and have to say the constant irritation with it is the gearing is to short.
However, 21k for a used machine is strong, I collect a new Tekna Auto with metallic on Wednesday which we've paid ÂŁ22,509+vat. via chalkes of Wincanton, obviously 0 previous owner full warranty and whatever miles its picked up being moved around the factory etc.
It boils down to how soon you need it though but if you were going manual I would probably wait if you were going auto then you could try and find a pre-reg machine with delivery miles for 21k+vat I'd have thought.