My only input would be war bonds not be able to be used to heal units. Units healed in battle by gold or war bonds are what hurts game play. Allow gold/bonds only to be used for infrastructure, plants, research, etc. Stuff for new items during the game and not for a player to cover up poor game play.
Another way to limit the use of Sabotage Buildings is to require a spy actually be in the province/city from the previous day to perform the instant action. That way a player can't cover up failed tactics so easily.