I think it would be neat if the NPC instead of paying in gold instead paid the party in Peerage favor points; as that is something all Peers would like and frankly the NPC seems like a scrooge and would love to avoid opening his coinpurse.
Personally I prefer gold. One can always buy potions from PCs.
What I think is lacking is better loot for the chests that require party members to open. They barely give anything.
Problem also is, how do you handle people who are not of the Peerage, like Mercs or Adventurers who came out to help? They have to way of truly benefiting from the Prestige, unless they join one of the noble houses.