I play in Europe and I've been working international magic values for years. I think the reason why in Europe we buy so many cards from the US is to do with WOTC pricing structure. At current prices a Shadowmoor booster box in the US is about $80 where as in Europe we are paying $120 (in Italy I paid $7 a booster last week). Because US sellers are not allowed to sell booster box's outside the US (a wizards policy) , we can only buy US singles. the high booster box price is passed on to the singles market and the prices are higher ( it has always been like this)

Basically what I'm getting at is that Foreigner's aren't affecting your price increases any more than before because we have always bought cards from the the US.