Just my thoughts on the last few posts in the other thread: small nations should be difficult to play. For almost all the times in history, being big almost always means being more powerful. There are only a few exceptions: city-states like Venice (compensated for their small size with a huge merchant network), countries which happened to be located in a very strategic position or on top of some very valuable resource (the Sultanate of Aceh and the modern Gulf States fit both criteria) and certain European states that became powerful relative to larger non-European states because of the Industrial Revolution.
Being too big does bring with it various administrative and other problems, particularly before the advent of the telegraph. Even so, it's rare that a large empire is entirely destroyed from within - you'll always find external pressure play the larger part in the downfall of most empires.
My $0.02