Is graceful degradation in the absence of JavaScript still useful?

Yes.

People can (and do) browse with javascript disabled. If your site will work without users having to explicitly enable javascript for you, that makes them happy.

Exactly how relevant depends on your target audience, of course.

Yes. Your web pages aren't just consumed by people: they're consumed by search engines, and crawlers, and screenscrapers. Most of those automatic tools don't support Javascript, and essentially none are going to generate UI events or look at deeply nested AJAX data. You want to have a simple static HTML fallback, if nothing else then so that your web pages are well indexed by the search engines.

Forget the crazies who disable Javascript; think of the robots!