Other than facilitating more rapid shooting (quite useful for sports, wildlife, etc), you're exactly right: The 1.3 crop mode is nothing more than an optical zoom. It doesn't really increase the "reach" of lenses. It just cuts down on the amount of sensor real estate being used. You can get the exact same result by cropping full images in post.
BUT...there is still real value in increased frame rates and longer bursts before filling the buffer, not to mention the value of having smaller files to transfer/manipulate in post, so I think it does have some advantages.