Is $HOME/.MacOSX/environment.plist still used in OS X 10.9.2 for setting global environment variables?

You can yourself ensure that this file isn't anymore used with a command as simple as ls.

Just end your actual session, and connect back. Open Terminal or xterm. Run the following command:

$ cd ~/.MacOSX
$ ls -luT environment.plist
$

The output of this command will display you when this file was last opened for reading. If it was opened by any process during your session start, you should see it thanks to the u option.

To learn more about the investigation possibilities of ls just run:

$ man ls

BTW, your environment.plist file doesn't use the right syntax. But this doesn't matter.