Back when we used UserVoice, I liked to occasionally browse the Completed tab and see what changes were made and features were recently added to the site. While I do think that Meta is ten times better at enabling users to suggest, discuss, and vote on feature requests, one of the downsides is that we are missing that feature.
The closest you can come is browsing the active tab. For the most part this works, but as the posts aren't closed or locked in any way, any activity on the post (edit, new answer, etc) will toss it back to the top of the active queue even though the
status-completed tab was added some time ago.
edit: I recently tried Kip's suggestion and, at least on Apple Mail, it suffers from the same problem that the Active tab suffers from. Namely, activity causes the RSS item to reappear with "UPDATED" in the title. Although it's possible to use another RSS reader with the capacity to ignore updates, I do think that an in-band solution is still preferable.