I think much of the reticence can be explained by previous South American centre backs, such as Alcaraz and Fazio. Had this been a number 10, we'd all be buzzing at the prospect, despite not knowing anything about him! I think it's natural to worry more about the defensive positions because there's so much responsibility on them so buying an unknown player from an area with a 'chequered' (perhaps harsh) history of defenders in our league raises a couple of alarms.
I'd rather we signed VVD, mainly cos I've heard of him and at least seen him play once or twice. Plus we know there's other interest in him so we'd have beaten others to his signature. Not that they're very good reasons but I think it's a default setting for a lot of us, working within parameters we're more familiar with. Even then, there'd always be the concern of coming from Scotland and would it be too big a step up.
Obviously, preconceptions or not, whoever we buy I'll be cheering their name. It may just take more for some players to convince us than it would others.