Nice idea, but no. We only get a better rate if we book through Disney US (therefore getting no advance buying). Disney UK and the UK travel agents don't price like that- the dining plan was more expensive to buy through virgin holidays than even a $2/£1 exchange rate (When it was $40 for US, we were getting charged $60). A Brit buying a UK Disney holiday in GBP is just as expensive (more for some parts if not all) as an American buying through Disney US in Dollars. When we get to the US then everything becomes half price- like food, etc. And, as someone else stated, no discounts, pins, etc.
Plus, (and this is a kicker) it is only comparable if you are a family of two adults and two kids. Most of our travel agents charge per person and not per room. So two adult in a room (same price as a family with 2 kids, right? No.) are charged under occupany!! We have to pay for the other people who are not in the room which can double the cost of our accomodation.
Sorry, but we don't actually pay half price for Disney. The only thing we get like that is when we are in the US and spend whilst there- that is where things are equivalent to half price.