And within a couple of days of posting this, LibreOffice has released a version that seems to do much of what I want! http://www.libreoffice.org

Maybe not perfect but, at first glance, it seems to be much more usable than the older versions. I will report back on it once I've played with it for a while.

Having done the export process a few times over the years, I've wound up with a lot of duplicates in Zotero thanks to multiple imports - not too tricky to delete the excess but more hassle than I need.

I've not yet completely removed EndNote due to the need to unformat citations before they become usable in Bookends, but much looking forward to killing it permanently. The only real, if minor, irritation so far is the lack of a keyboard shortcut for inserting citations - I prefer not to use a mouse. I'm pretty sure there's a way to get around this but it will probably involve a bit of Automator hacking.

I can't seem to get the keyboard shortcuts to work in Zotero either...

I've found this - http://veritrope.com/tech/the-basics-using-keyboard-shortcuts-with-applescripts/ - which seems promising. Not tried it yet but the option to add context-sensitive keyboard shortcuts looks like it should be an answer.