Update: After consideration of our timeline and what is likely to lead to the most satisfying result for players, we've decided to cut tactical battles for now. It's just too large and separate of a "minigame" to really fit with the larger game, and so we're going to think about alternate ways to get your NPCs to help you, so that helping them isn't just a "trophy system" but actually matters longer-term in a gameplay sense. Tactical battles may well return at some point in the future, but for now they're out of scope and we're going to do something simpler and more existing-game-integrated to accomplish a similar effect. Once we figure out what that simpler thing is. 
Well you could always have a mini version of that and just have the ability to bring one or two other npcs along with you? I know what you mean though, I don't think my above idea is particularly interesting...
Honestly the only other idea I have is relationships....but you did say that was something for an expansion. Relationships and giving npcs more life and human-ness would likely lead to making it easier for them to come across as important and having a purpose. I'm guessing relationships would be even bigger to implement than tactical battles though.
It would be neat some day if npcs could develop relationships/links in the background though. Also if npcs could have standings in society, like peasants or upper class. Then some npcs would be like VIPs. (royalty or whatever AVWW's equivalent would be)
Different groups of npcs join together (like some kind of system that is procedurally generating guilds/groups of npcs/monsters working towards some kind of cause.)
All of the above would happen completely in the background, so you could choose to completely ignore it if you wish.....or you could meddle in their affairs.
I'm feeling now that's not really the answer to your question. When it comes to how characters work socially/psychologically in games I get very excited.
