Besides the them itself I've always liked those old LEGO castle sers because of the ability to attach different sets together to build even bigger castles. Now that I have all the sets (even multiples of some sets) I have been finally able to fulfil one of my childhood dreams.
But even with all the sets there isn't enough to "complete" those huge castles. Sure additional copies help, but just attaching similar sets end to end gets a bit repetitive. With some duplicates there is also alternate original builds that adds to the variety. With some sets that don't have that I have build the extra sets as mirror images of the actual set. It's a nice extra challenge trying to follow the instructions, but turning the build around so that it mirrors the original.
I've also had a problem with some sets that I never completely liked because they are just facades, half builds where the backside is open. Of course this can be considered as feature as it helps the playability of the set when you have easier reach to the inside. But for display purposes it feels a bit hollow to me. But luckily that is often also easily solved if I have two of the sets: just build the other one as mirror and stick the halves together.