Is there an Android calendar with limited security permissions?
To answer my original question, I've found aCalendar, which has very limited sandbox requirements. It just asks for Your Personal Information, which it needs to write to the shared calendar store - impressive! As I've said elsewhere, this leaves calendar items prone to accidental synchronisation with Google, but for most people this is acceptable.

Happily, the UI of this calendar is excellent, with only a couple of niggles (in particular, the small screen of the Europa makes it very difficult, occasionally impossible, to touch on calendar items in the 7-day view). Issues aside, I am likely to settle on this app, unless a better one comes along!