I started a 2 months and i love this game as a history nerd this right up my alley. These are few more suggestions I am sure you have thought of ..
1. A buddy list or friend list esp for frequent and longterm players
2. Rating list or reputation list
3. Mid-game or end of game polls or awards : The most Machiavellian or The Schlieffen Award best strategic, players best villain, best ally, maybe a few fun awards displayed in the paper players get to vote . Players submit their own polls in the paper that could be fun.
4. When you are being invaded a def army should be able to destroy an airfield or factory perhaps just damage it .
5. As a spy gains exp the spy can perform more targeted attack this of course leads to greater danger of being got...it would give the smaller country a shot.
6. It would fun if a Sub can covertly attack troops ...
Thanks just few ideas Thank you