Honestly I think owning a castle in an RPG is way overrated. The reason castles are cool is because of fighting back sieges and ruling as a lord. You do neither wandering the world as the chosen one. Fighting back those pathetic redshirt raiding parties with your pathetic NPC redshirts in the courtyard don't count as invasions btw.
Another cool reason for owning a castle is building and furnishing it yourself, but the upgrade system is a very dissatisfying implementation of that aspect.
You should have some way to own an awe-inspiring home just to signify how truly important you are, but finding a random castle and not doing anything with it doesn't fulfill that purpose. It'd have been better if you were awarded a great villa in Brackenbury in an official public ceremony where you're hailed as their hero. That'd have been seriously awesome! Or it's more awesome as a general mechanic, I guess it wouldn't really fit the plot of the game in his particular example. To be honest, after I did everything castle-related... I'd think the game equally great without any castle, that's how forgettable it is.