I've been pondering how to do a 50/50 with plists considering that ganbustein says its extremely unlikely to work, particularly in the most recent versions of OS X, and I think I've got it...
Do a command-D on ~/Library/Preferences, and drag the copy to /Users/Shared. Then log in to a test user account and copy the individual plists from /Users/Shared to ~/Library/Preferences, 50/50 or otherwise, until you maybe find the culprit. (You probably ought to check permissions on the plists.)
Edit: I think that works...haven't tried; I tried with a guest account, and OS X wouldn't let me do it.
And on the subject of permissions, do you think there's any possibility that repairing your home folder permissions is worth a shot?
Last edited by artie505; 01/09/15 12:44 AM.