From what I have been able to figure out there are only two places (read folders) that get updated, for pretty much every update. All other folders dynamically generated/updated. The folders that get update are the main wow folder (typically "C:\Program Files\World of Warcraft"), and the Data folder inside the main folder. Since the data folder is Symlinked, all you should need to do is copy all files from the main folder in your main, to the main folders of your alts.

Hope that wasn't to confusing. Also, check out Lazyboxer .