Regarding whether spit is just spit:
My opinion is that if there's anything in the movie that stands out enough for us to notice and comment on it, it most likely means something. And if an object (or, in this case, an action) is significant in one scene, then the object or action is also significant in another scene -- not necessarily in the exact same way, but in a way not unrelated to the first way.
Am I getting too convoluted?
Yes, in real life spit is sometimes -- pretty much always -- just spit. And snow is snow and buckets are buckets and bears are bears and moons are moons and beans are beans and fans are fans and cowboy hats are cowboy hats. Not in the movie. The filmmakers may occasionally let logs disappear and microphone cords show, but they are very very careful when it comes to symbolism and metaphors, and everything is worked out really thoroughly. So they wouldn't make a big deal of connecting a symbol to a meaning in one case and then in another scene -- oh well! -- just stick it in for the hell of it, or let it exist because, after all, people do spit and encounter bears and use fans and wear hats. (Note: OK, I guess I wouldn't try to argue that, say, every single cowboy hat on every single extra in the movie has some shattering resonance. But if a hat is prominent enough to be noticable, it's probably so for a reason. If in the last scene we see a huge fan propped on Ennis' bed, it's not just because the nights have been hot lately. And if someone conspicuously spits ...)
It's fun to figure out which symbols mean what, but I don't think they're there just as a fun puzzle, like a sudoku (sp?) game. They're supposed to deepen our understanding and appreciation of the movie, often on an intuitive level. So if a symbol conflicts with your intuitive or emotional reaction, Mel, then that means your reaction is wrong.
Just kidding!!!! It means that maybe the symbol is supposed to represent something in a different way than people are saying. For you, anyway. In other words, I think you should trust your emotional instincts first.