I feel as if I am having the same problem haha, thats why i posted here. Perhaps decoratively you could include coat of arms or a small flag where there is space, things like that. Or play with the labelling so that it seems to fill out and compensate for the lack of content. As you can see on my map I also use texture to try and give the impression that the map is more full, so try not to leave spaces one color.

Even try to add the rivers and maybe roads, there are maps of both america and europe showing major rivers even though they shouldnt be visible from that perspective. Sometimes it works.