So, I had a brainwave on how to make "Best Interests" have a little more teeth (and only after writing it down did I realize it's a solution pretty close to the Burning Wheel system I'm finally getting around to reading).
Not only will it give the best interests more mechanical weight, it will (hopefully) increase the tension of choosing between differing interests. Here's my thought: you've got three best interests (individual, family, and clan) and three resources. So completing interests gives you points in a resource!
The run down (until testing makes me decide to do otherwise) is that fulfilling a clan best interest gives you a wealth point, fulfilling a family interest gives you a loyalty point from one of your family members, and fulfilling an individual best interest gives you a glory point. I'm afraid that the family interest may be getting the short end of the stick here, as the loyalty points with your family members will only come up if you try to get them to help you out in conflicts, but hopefully that will come up in play.
I'm also not positive on how to judge interests "fulfilled" but since all interests are player generated, I'm thinking the GM decides when they're fulfilled. This is part of a general swing back towards more GM authority that I'm thinking will happen having considered the game more recently, since I was all high on hippie authority sharing as a brand new concept to me when I wrote the first draft of the game.
I need to give the whole system a good once over before I get the chance to do some real live, in person playtesting sometime in the next month. I am very excite.