Does Wow still launch and "authenticate" after changing the plist file? I had issues with the application not passing what i assume was some type of checksum verification after modifying the plist file, But that was 2 + years ago. They may have changed it since then.

Here is what i was using back then to launch and position my windows, if it helps anyone. I had to have a separate preference file that stored the correct window location for each account.

I have to say that your method is much cleaner.

Code:
tell application "Finder"
    open application file "World of Warcraft 1.app" of folder "World of Warcraft 1" of disk "Media"
end tell

delay 2

do shell script "defaults write NSGlobalDomain AppleDisplayScaleFactor 0.86"

delay 2

do shell script "cp -f /Users/username/Dropbox/Docs/5Man/2Shadewalker/com.blizzard.World\\ of\\ Warcraft.prefs /Users/username/Library/Preferences/"
tell application "Finder"
    open application file "World of Warcraft.app" of folder "World of Warcraft" of disk "RAID"
end tell

delay 4

do shell script "cp -f /Users/username/Dropbox/Docs/5Man/3Eternalchill/com.blizzard.World\\ of\\ Warcraft.prefs /Users/username/Library/Preferences/"
tell application "Finder"
    open application file "World of Warcraft 2.app" of folder "World of Warcraft 2" of disk "Media"
end tell
delay 4

do shell script "cp -f /Users/username/Dropbox/Docs/5Man/4Tartare/com.blizzard.World\\ of\\ Warcraft.prefs /Users/username/Library/Preferences/"
tell application "Finder"
    open application file "World of Warcraft m.app" of folder "World of Warcraft" of disk "The Void"
end tell
delay 4

do shell script "cp -f /Users/username/Dropbox/Docs/5Man/5Animatedead/com.blizzard.World\\ of\\ Warcraft.prefs /Users/username/Library/Preferences/"
tell application "Finder"
    open application file "World of Warcraft 3.app" of folder "World of Warcraft 3" of disk "The Void"
end tell

delay 4
do shell script "defaults write NSGlobalDomain AppleDisplayScaleFactor 1"