I agree that it doesn’t feel like there is a huge amount to do. It isn’t just being motivated by fights, but the rewards for are much less defending than attacking.
My suggestion would be to allow someone inside a location to become the Tower/Keep/Castle officer. While within a radius of this location, the officer has options and abilities open up. These benefits could include:
a) The ability to call upon the nearby NPC camps for reinforcements. If they are not friendly, then you can send guards/scouts on missions to bring them on your side. Tiers of friendship affects how many reinforcements they send. High tier local NPC camps also provide supply.
b) A moral system – the officer can provide buffs and shouts to player and NPC defenders. Equally if he/she dies, this adds a penalty to friendly players and NPCs.
c) Sending out scouts. This allows the local-commander to send out scouts to provide more warning of incoming attackers/zergs. Scouts also lay traps to slow down or interrupt enemy players.
d) The officer’s party. Those joining the officer’s party receives perma-buffs while within the location.
e) Set priority-status for the location. This helps other nearby players know how they can help. Whether it is to get more supply, capture camps, and so on.