Hi All,
It's something much more subtle than the system/user font location. On my system, despite Kieran's success, it does not work, and when K upgrades the mac it may not work for him. In correspondence with the typographer of the font, we have all definitively established what the correct version is.
This matter is specific to Alegreya, to the Mac, and to lilypond using it, not other programs. It does not arise with any other font that I know (but it is hard to test hundreds of thousands...) and does not arise on Windows or various Linux distros.
I don't regard this as done and dusted yet. It fails on a Mac pristine install for High Sierra. This is not good at all. I'm am continuing to look further into this very pinpoint specific failure pattern. It's odd.
Andrew