Population wise, Scotland is about the size of Slovakia, Denmark, Norway or Ireland. I’m not sure any of those consider them selves to be a “non-entity”.
No but then a little yappy dog thinks it’s the business, doesn’t mean anyone else takes any notice. That’s why nearly all the small central and Eastern European countries are acutely aware of how important it is for them to be integral members of the EU and NATO, rather than create a different minor union between themselves.
If you genuinely wanted a Celtic union type thing, you’d be better off going all out for Scottish independence then join the EU and use the tools that come with that to build closer links with Ireland. Sort of like how the EU has facilitated close cooperation between the Baltic countries.