We've got a page with a ton of jQuery (approximately 2000 lines) that we want to trim down b/c it is a maintenance nightmare, and it might be easier to maintain on the server. We've thought about using UpdatePanel for this. However, we don't like the fact that the UpdatePanel is sending the whole page back to the server.
jQuery AJAX vs. UpdatePanel
Please don't put your self in that world of pain. Instead use UFRAME which is a lot faster and is implemented in jQuery.
Don't move to UpdatePanels. After coming from jQuery, the drop in performance would be untenable. Especially on a page as complex as yours sounds.