Figured it out. I actually did have a previous version of the SDK tools/Cmd installed with Sencha 2.0. So I used its uninstaller and re-installed the latest Cmd (v3).
But I then got 'command not found' error when trying to run the 'sencha' command. Luckily, I found this post on the forum which explained that, at least for Mountain Lion, I had to add to my paths list and add a sencha command environment variable. I added those to my .bash_profile and now I can at least fire up the basic command.