Doesn't it really come down to knowing your market? A writer's style should appeal to the author's target audience. I could easily envision a story written for one market and then edited with regional-isms for a different groups of readers in another country. It's almost like translating a novel into another language. This applies to unusual spellings as well. For example, many fantasy genre fans might actually prefer old-world, anachronistic spellings that lend a certain "feel", or ambience, to the story. So, the answer to the OP is simple. Write to the target audience, using spellings that will be most suitable to achieve a desired effect. There is no "right" or "wrong" spelling; only appropriate to a given market, and as others have noted, consistency is the one rule that must not be broken. Readers don't mind adjusting to an unusual style once, but twice or more in a story makes for frustrated ex-fans.
