You asked if there is a point to spend the night.......Dromoland would be the perfect place to stay overnight, as while it is a castle, its purpose nowadays is a hotel. It's not a place that you would tour room-to-room. If you do not stay as a guest in the hotel, I am guessing you could purchase lunch or dinner there and maybe able to tour the lovely walled garden, but best to call them ahead to ask. But, great place to spend the night.
Another fabulous place to stay is Ashford Castle, which was the home of the Guiness family. It was voted one of the top 5 hotels in the world last year. It is fabulous! If you are looking at a map, it is in Cong (which is roughly north of Galway).