> When have most users ever enjoyed a new UI in a system that they're used to?

Blender.

Is has seen some drastic changes in UI but barely any backlash. Even holy-cows like right-click select got mercilessly slaughtered and I am not even mad about it, in fact I love the changes.

The main thing is that they are focusing on providing value to users and are dog footing their own software to create movies.

But yeah, generally people hate change and you should avoid changing things as much as possible. Sadly that doesn't work with the way incentives in most companies work.