I'm a long-term Inkscape user, they recently 'improved' the icons; it all looks wrong (but handsome in a minimalistic, low-visibility of chrome, sort of way) and disturbs my workflow considerably.

I'm not sure why the parent comment was downvoted. If the above statement was intended to mean that being consistent and intuitive is more important than aesthetics then that is almost certainly true, in my experience designing and testing UIs. Of course, the ideal is to have it all by using the aesthetics to support the functionality. Being attractive and being functional aren't mutually exclusive.

This is where, IMHO, a lot of generic minimalist/flat designs following the current trend go wrong: they sacrifice so much detail and so many possible ways to be visually distinctive or interactive that what remains inevitably all looks very similar and loses some of the visual cues that could help to guide the user in how the system works.

But being fashionable and being functional are often opposing forces.

Seems to me flat web design was a reaction as the antithesis of an over-indulgence in skeuomorphism. We just appear to have thrown out a lot of affordance and visibility in that reaction.