FranticFish - 11:42 am on Mar 9, 2012 (gmt 0)
Thanks for sharing your experiences. My two cents:
I've been slapped once for doing this in the past, when I changed the title of a site to match the phrase the home page was already heavily optimised for and was the sitewide anchor back to it.
I believe the difference often lies in an overall website historical picture, coupled with a current total profile that folds in a couple hundred factors
Was either home page (or site) already fairly aggressively optimised for that term?
Then when it enters the page it finds nothing new, so you've changed title to rank better.
Recently I've only ever done title tweaks when adding extra content to a page - or at least changing the content substantively, and I've only ever seen positive results from doing the two together (albeit in some cases gradual).