I haven’t managed to justify them as an essential part of my interface design work either. Yet. Hasn’t stopped me trying!
I can see potential for creative use as tangible artefacts (3D personas or scenarios?), as unconventional molecular gastronomy for the meeting room lolly bowl, or in prototyping or modelling specific parts of an experience, especially where dealing with offline products. But they still feel like cool geeky gimmick uses, rather than a serious use of project funds. Not that I’d ever let that stop me.
In a more abstract sense, being creative, exploring, solving and tinkering with things is part of a designers job / spare time.