Here are some points of congruence I see:
- relationships matter. The strongest conflicts are between characters that have some sort of relationship.
- characters do best when they really show their traits--even when their traits aren't obviously useful ones. (Episodes like "The Zeppo" make a lot of sense if you think of Xander having a trait "Normal Schmo: 3d10".)
- the patterns I talked about in this comment fit: the most intense conflicts are between characters that have a long history together, and it's very possible to fail mutliple times and come back stronger.
- weaponry and gear matters, but it's far from decisive; you can bring a knife to a gun fight without automatically losing.
There's a lot to be said for giving more time to the Western law-enforcing setting, and there's a lot to be said for trying out the Buffy RPG rules. But this combination looks like it might go very well together.