Indeed. Would Winksy playing for Spain be a good or bad thing? It'd be great for his personal development, and therefore (hopefully) his effectiveness in the heart of the Spurs midfield. It'd be England's loss but, having seen how the likes of Hoddle, Scholes and even Carrick were utterly misused by England, is that such a bad thing?
Would he still count as a homegrown player?
Well, from a Spurs perspective, I don't trust the England setup with our players one bit. They tend to come back with inflated egos (having had their heads turned by the lads from bigger clubs while away on international duty), injured, or with their reputations tarnished on the back of a typically woeful Euro or WC campaign. Plus, as you say, they don't have a great record of managing skillful central midfielders or favouring team cohesion over star players being stuffed into any formation that allows them all to be on the field at once.
In that regard, Spain *might* be the better option - it's hard to imagine Sergio Ramos or the Barca phalanx sidling up to Winksy and tapping him up in *quite* same manner, and his technical skills and tactical nous would be improved much more by playing alongside Spanish players and under Spanish coaches. It's not a perfect option, mind, because he might have issues fitting into the Spanish setup and the Spanish press might give him a lot of stick if it ever got that far..but it would possibly be better than wasting his international career being benched while Rooney plays in central midfield at the age of 45.
However, that's just looking at it from a Spurs perspective. Ultimately, if he feels English, he should play for England, or wait for England to call him up - none of this 'Irish/Spanish/Cameroonian on my grandfather's side' stuff if he genuinely feels a part of the country he was born and brought up in. I respect that people can have differing feelings as to their identity in this postmodern world, and that football might be a career option to players that entails searching for national teams to gain caps with as easily as they search for clubs to play for - but it just doesn't sit right with me all the same, and I think that, if I take the Spurs glasses off for a second, he should probably go with England even if he doesn't get as great an international career out of it.
Edit: although, to be fair to him and people struggling with the choice to play for England or A.N.Other, it's complicated by the fact that the UK allows its constituent units to have separate football teams, I guess - it might be more cut and dried if it were a choice between just a GB football team and another country's NT. He might well feel more British than English.