I don't think £4k is out of all reason for that car from a dealer. And if you've seen it in the flesh, driven it and the service history is good then go for it. Dash could be a cosmetic repair and you might be able to fix the tailgate yourself. MOT history is OK but factor in some suspension work. I'd also check all the dash lights come on and go out at start up. A fault is mentioned in the history. Make sure someone hasn't just disabled the bulb.
I wouldn't compare to a 350 because they're nearly double the road tax and also people do forget that dealers are doing this to make a living not out of the goodness of their heart.