Frankly, if you're trying to tell someone else what should be relevant to them then you're talking crap. You can't know what's relevant to someone. De gustibus and all that...
Re race memory, do the majority of Americans not have European origins? Was the country itself not founded by English-speaking Europeans? Given that, all American musicians have some roots in European music. They'll also have links to whatever else they've heard (black slaves with songs from African origins, etc). So when those American songs go back across the Atlantic via Paul Simon and Bob Dylan, are Europeans not then allowed to pick up on the new versions of the old stuff? Or are they only allowed to play the Bob Dylan songs that have recognisable English influences in them? And even blues songs can often be traced back to older broadsides or traditional lyrics, so what then?
Would you have told Django Reinhardt that he couldn't play jazz because it originated from black musicians? And would you then tell all current American jazz guitarists that they can't try to play jazz on guitar because Django Reinhardt did it first?
As far as I can see, the main people who are *really* keen on keeping a culture isolated are immigrants who come to another country, feel isolated, and gang together with other similar immigrants against the rest; or those who feel threatened by those immigrants. In that case the culture becomes a definition of us-versus-them. You only need to look at how fanatically the Orange Order proclaim themselves to be British, or the Boston Irish (or in fact most Americans who say they're "Irish" or "Scottish").