Here’s an idea for your review. Give each country abilities to allocate spending in diplomacy, research, and intelligence. Cards could be made like this for each country and placed on the table:

Chips can then be purchased and put in each circle. The chips in the diplomacy circle represent the number of diplomats you have. The chips in the reseach circle represent the number of scientists you have. The chips in the intelligence circle represent the number of spies you have.
DIPLOMACY - Choose a neutral territory to negotiate with. Roll one die for each diplomat you intend to use to influence that territory to join your side in the war. Any sixes you get mean a possible breakthrough. Any one of your opponents may then try to roll an equal or greater number of sixes for his diplomats to block the breakthrough. This circle could also be used to do such things as negotiate a separate peace with a country.
RESEARCH - Roll one die for each scientist you have. Every six is a potential breakthrough. One of your opponents can then roll for his spies to try to sabotage the breakthrough. An equal or greater number of sixes rolled stops the breakthrough.
INTELLIGENCE - Your spies have the option of doing one of two things during your turn.
- Kill your opponent’s diplomats, scientists, or spies. Roll one die for each spy you have. Any sixes rolled potentially kills an enemy diplomat, scientist, or spy of your choice. Your opponent may roll for his spies too - any sixes rolled blocks the action.
- Steal your opponent’s research breakthroughs. Each six rolled potentially allows you to steal one breakthrough. Your opponent gets to roll one die for each of his spies. Each six rolled blocks this action.
- With this system you could do possible things with spies like blow up an opponent’s ship or assassinate an important leader, causing a morale drop and economic penalty. The system is only limited by your creativity.
This idea was gametested with mixed reviews - some thought it took too much attention and resources from actually fighting battles. I suppose this could be fixed by adding income.