I think a TODO app would be an instance where the benefits of a "full client-side application" may be significant enough to outweigh the downsides, for the good

I think a TODO app would be an instance where the benefits of a "full client-side application" may be significant enough to outweigh the downsides, for the good reasons you describe. I was a bit imprecise in the portion of my comment that you quoted; it was mainly a response to the parent's assertion that there was no reason to hold back from using JavaScript, even on his/her blog.