i think if you already have art and are happy with it, all you need are a couple of statement pieces to jazz it up a bit - something beautiful and unique to go on top of the table, a bench or something similar to go against the back wall below the art, and a sculpture or something like that (like the rocking horse in the pic above).
what kind of frames do you have on the artwork? playing around with different types of frames is also cool, you can look around for different types of antique frames and mix it up a little, especially if most of the pictures are by the same artist. you also said you have old maps and stuff on the walls. i think it would be fun to mix up maps and pictures and other framed documents, in different types of frames, so it doesn't look to 'matchy'. sometimes it's just about rearranging what you already have in a way that draws the eye.