There are various people who feel that Lesswrong degraded in the last year. In the same timeframe more and more discussions moved into the open thread model and open threads became weekly instead of monthly.
I suggest to counteract that trend by opening all discussions per default on Discussion instead of opening them in weekly open threads. Having the topics in discussion makes it easy to browse the list of topics and choose the headline that are of interest, even if the thread got opened two weeks ago.
As several people have pointed out, the problem is high barrier to good posters, like Yvain. For various reasons either practical or emotional or whatever they don't post anymore. However, many of the quality Commenters, as opposed to "posters" hang on. Removing Open Threads won't do anything to get people to write interesting Posts, unless you think there are a lot of open thread comments that should be posts. It will just reduce opportunities for quality commenters to talk to each other.