I am viscerally against this concept.

It's one thing to include the spelling as a way to capture the phonetics of an accent or a dialect, entirely another to accept its use in writing when using a neutral voice.

If anything, because it's so often just a misspelling I would avoid trying to use it as a phonetics thing just as a matter of style. At this point everybody would think I'm making a mistake instead of trying to mimic a way of speech in a way they'd never do with "coulda".