I have a sailing friend who is the parts manager at Grand Touring. He says that the Aston's are very good now compared to the past. While they start chasis life the same as the Jaguar they are a totally different car, especially the DB9 with the 12 cylinder. Have you heard this at full wail?
While parts and service are expensive he did say that for a low mileage daily driver it is OK. By the way anything in that price range is going to cost a lot for parts and service. In fact VW has some of the most expensive parts and they own Bentley. Remember who owns Jaguar now. Aston is now back in the hands of a true car enthusiast.
Are you dealing with Dean Jordan at Grand Touring? He is excellent and comes from the factory so can give you a lot of inside insight into the car.
Good luck and please please bring out the DB9 to a get together if your dad pulls the trigger.