I completely rebooted, no change. "Open In Low Resolution" still checked and grayed. I tried manually editing the plist file. No effect. (The file *is* setting the NSHighResolutionCapable key to true, BTW.)
Right the new .plist files are good after installing the update, but you have to get OS X to use the new one instead of reading the old one from cache. I had to touch the .app files in Terminal to get it to work. Logout/login and full reboot didn't work for me.
The update is probably working for some people if they haven't run an Office app for a while, and there is no cached .plist being used.