It inspired Win95. It inspired the original Netscape browser's UI (toolbar etc is very NeXTSTEP-inspired, not surprising because it was developed on a NeXT box). It inspired the Mac OS X and the iPhone, although both have degraded since then. As things exist today, NeXTSTEP from 40 years ago (!) looks much nicer - and way more usable - than today's flat UIs.
Widely? You seem like the only one carrying the water for nextstep. I'm sure they had some advances but overall it's a very ugly UI.