What I plan on doing in my next campaign is rather then give all the AI a cash boost I will increase the kings purse of a select few. I find that after you have beaten the factions that directly border you it is simply a matter of steam rolling the rest. However, if you give just a few A.I. factions, that are far away from you, and each other, a large King's purse you can create other super powers to challenge you in the late and mid game.