toggleSaveStream button template
From looking at it, the name of your function toggleSaveStream is lying, calling it twice will not make it toggle, it will look at the the status of the user and set the status accordingly. So I would simply call it updateSaveStreamButton.

Since it does that, you could call it at first, de-activating the button, and then once the user is loaded call it again. 

Then you would simply have

&lt;button id="saveStream" class="button-icon button-small save disabled&gt;" title=""&gt;


And then

initialize: function() {
    this.updateSaveStreamButton();
    this.listenTo(User, 'change:loaded', this.updateSaveStreamButton);
},

updateSaveStreamButton: function () {
    var userLoaded = User.get('loaded');
    var templateHelpers = this.templateHelpers();

    this.ui.saveStreamButton.toggleClass('disabled', userLoaded);
    this.ui.saveSelectedButton.attr('title', userLoaded ? templateHelpers.saveStreamMessage : templateHelpers.cantSaveNotSignedInMessage);
}


This sounds too easy, so feel free to point what I am missing ;)