Levenshtein Distance is used all the time to compare words with each other. When you do a search in a web page for example, the Levenshtein method is used to compare what you search for with all the words in a page.
We can use this same principle for calculating the difference between varieties that we have word lists of. It's a relatively new area of application and there aren't many survey teams using this method. However, it holds a lot of promise, if you can figure out how to apply it.
Something that might make it easier for us to use it is a promising piece of dialect mapping software called Gabmap
For more info, read the paper by Karin Beijering, Charlotte Gooskens and Wilbert Heeringa online