Not specifically to do with the football, but as a 16 year expat Sais resident in Wales, I see a very fundamental difference in the styles of English nationalism - which utterly manifests around football - and Welsh nationalism (which, TBF, also does to a lesser extent).
There have been a few times over the last few months - around the Euros, and other things - where the issue of Welsh national identity has come up amongst groups of people I have been around. What the Welsh - and for all I know, every other country in the world apart from a certain section of English people - seem to manage to do is to cherish a fiery, assertive nationalism, without it turning into something nasty and vindictive, something I've always felt deeply uncomfortable about around the English variety.
Case in point. There was a musician in the neighbouring bar, and at the end of the set, he moved on to Welsh nationalist songs. I'd not encountered Dafydd Iwan before, and the guy sang "Yma O Hyd", and one of my (Welsh) friends was translating it for me, to the mild discomfort of some of my other Welsh friends (note for non-Welsh speakers: it's a pretty blatant gesture of defiance and a call to arms for the Welsh against the English). I think they were more worried about how I'd take it than their feelngs. The point of this is that, defiant and aggressive though it may be, Welsh nationalism (for one) is not about hate, supremacy, and destroying anything in its path.
And welcoming. I am blatantly English, and I have only ever had the mildest anti-English prejudice shown against me in all the time I have been here. Sure, Wales does have racism - but it doesn't have that same pointed sense of entitlement that English racism seems to bring with it.