By my faith! For more than forty years I have been speaking prose without knowing anything about it, and I am much obliged to you for having taught me that.
We have been doing AHAH for a few months and now I know! The thing definitely makes sense, especially as the app gets more complicated and every bit of code shaved off the client side saves us a bit of our lives.
The performance still requires investigation. For now I assume that transparent gzip compression can make HTML snippets just about as small as compressed JSON responses.