Often times I find myself creating calculated fields which have same logic, but the literal fitler condition is different. If a Copy or Duplicate option is provded it would reduce a few steps and make development faster.
This is a great feature request. +1. In the mean time this Chrome Extension, QuickSight Power Tools may help (if you have access to temp credentials with privs). It will let you quickly export/view all your calc fields without opening them in the UI.
I may look into adding “duplicate calculated field” to the Power Tools.