iTunes, even when not playing, keeping my computer from sleeping automatically
I called Apple and interestingly the stuff they advised me to do was nothing I'd found anywhere online. They said the issues with coreaudiod are generally caused by iTunes extensions. They had me open up Activity Monitor and advised me to kill a process called AccuBeatMix, and that made the issue go away. I've got an e-mail out to the maker of AccuBeatMix to see if there's a workaround and will post here if there is. Until then I've just got it uninstalled (moved it out of /Library/iTunes/iTunes Plug-ins).