Any Welsh blood is worth having!! Most of us are mixtures off all nationalities, if we go back far enough. I am 100% Welsh, and all my immediate relatives and ancestors were Welsh-speaking. I've done a vast amount of my Family History over the years, and haven't found a single ancestor who wasn't born in Wales, or spoke English as their first language.
Naturally, I'm very proud of my Welsh heritage, although I've lived in England for 47 years, and am married to an Englishman who, fortunately, understands and supports my innate patriotism.
When all is said and done, it's what we are, and how we behave to others on a daily basis, which is important, not just where we originally came from, but a bit of friendly rivalry when Wales plays England doesn't do any harm!