>why do you think it's useful for users to read meta descriptions?
It isn't, really. I made a mistake and thought that every page (served to users and search engines) had the same title and description. A user is unlikely to read a meta description, unless he/she is on a search results page.
>How does making this a pure JavaScript web app degrade the end-user's experience?
NoScript users and special need users are unable to access your website's content.
> JS and client-side rendering makes for a much better experience.
Agreed. Progressive enhancement makes this possible and get the best of both worlds: Accessible content for NoScript users, spiffy JS rendering one page app for JavaScript users. RMS can even download your pages through Lynx.
If you go pure JavaScript, you can at least add a <noscript> where you explain why you need JavaScript to enjoy this site.