Maybe allow user to control what bonuses he gets??
Have a set "number" of points user can put towards effects, and give him 3~4~5 effects he / she can choose. They can put all points towards unrest, or all points towards production, or make it an even distribution amongst all 5 effects, all weak, but all positive, or 1 strong, others doing nothing?

This allows player to cast this spell more than once? Maybe at greatly increased upkeep cost with each cast (an exponential increase, as such?) First one is cheap and easy, 2nd one is a good chunk more expensive upkeep, but a decent sized empire could keep it going, 3rd cast is downright extravangant and only the massive empires with extreme income could afford to keep that thing going, etc.