Over on System San Setting Mass Effect 3 is brought up as a way to make NPCs matter - have them grant some sort of in-game effect, i.e., rescuing Baron Gets-Lost-A-Lot grants you access to his cavalry for future endeavors, or Bailing Sir Never-To-Do-All-That-Well out of a tight spot makes his sister, who is married to the king, give you a bonus to all your attempts to convince the King of your plans.
What caused my head to snap was the line "there are few elements of player psychology more powerful than the act of putting something on a character sheet," and I went really? Cause my players are fully capable and have ignored such items. But I think that says more about my players' engagement with the system (there's a reason why that attempt lasted so little time) than anything else.
But assuming you have buy-in, this sort of NPC so-and-so requires a certain amount of gamification of the arcs. Where players know going in what the stakes are "Well if you do this, you'll get this sort of reward," and feeds best into something beyond the straight kill monsters for the glory and safety - where there's a larger meta-game at play of various power groups.
Combat and wargaming are the easy ones because social conflicts are so nebulous to describe and to provide tactical advantage for. It is easy to make the Baron's cavalry more impressive and useful, but how do you quantify boons? (Okay some games, such as Cortex+ where the boon would be an asset to improve the roll it is easy, but there's more than one reason why the Cortex+ line is seducing me with its siren call.)
Eclipse Phase does it with Rep gains, which are basically currency in the post-scarcity age. I could see Fate doing it with an Aspect with a free tag or two to hit to shift a crucial roll.
But I'm sort of stymied at this point. Cortex+'s solution, a persistent asset seems to be the most reasonable one of the bunch; however, it is tied into the system tightly - I come back to "And there needs to be some sort of secondary game where these resources come into play" which brings me back to the system of Reign, which while it did not work for my group, did provide a nifty state actor versus state actor venue to play in.