I always viewed culture as far more fluid than a lot of people want to accept and I think you hint at that a little bit here. It is easy to tie our identity up in a culture but it is an intangible concept and no two people, even within the same culture, interpret it exactly the same. This is one of the reasons that I always thought it was a bit silly when people get bent out of shape over "appropriation."
As for myself, it is hard to pin down. I find that I can "slip" between several cultures. Border culture, Southern culture, academic culture, ghetto culture, psychedelic culture, weed culture all have something that I view as part of my culture but I can't say that I really fit into any of them very well.
The only thing I think is worth calling appropriation is when people actively try to cash in on a certain culture. If our culture didn’t encourage the commodification of everything down to our very personalities, appropriation wouldn’t be a problem, we’d all look at someone who had dreadlocks or a nose ring or whatever else in order to create a kind of image as a bit of a tool. Authenticity makes the whole issue redundant.