As for the reasons why EY considers the MWI advocacy being important to applied rationality, they are explained in the earlier reruns. Can't say that I agree, but many regulars do, so more power to them.
I don't recall any regulars expressing agreement that MWI advocacy is important to applied rationality to the degree suggested by Eliezer. (It could have happened but it would look odd to me.)
Anyone bothering to try and determine whether this is true or not needs to know your definition of "regular."
Today's post, Living in Many Worlds was originally published on 05 June 2008. A summary (taken from the LW wiki):
Discuss the post here (rather than in the comments to the original post).
This post is part of the Rerunning the Sequences series, where we'll be going through Eliezer Yudkowsky's old posts in order so that people who are interested can (re-)read and discuss them. The previous post was Why Quantum?, and you can use the sequence_reruns tag or rss feed to follow the rest of the series.
Sequence reruns are a community-driven effort. You can participate by re-reading the sequence post, discussing it here, posting the next day's sequence reruns post, or summarizing forthcoming articles on the wiki. Go here for more details, or to have meta discussions about the Rerunning the Sequences series.