I'm in a similar position. My wife and I have a 11-month old baby and evening going away for 1 night necessitates that the rear seat is used for luggage. This perhaps says as much about my wife's packing as it does the size of the car. Either way though, when we have a second child the car just won't hack it.
My car is also an import from the Netherlands. It's an 06 with just under 30,000 miles on it. We've been looking into buying a new 3.0 V6 Touareg next year, which will hopefully satisfy the needs of the family until the children are grown up, however my first impressions of how much my GTI is worth doesn't make it worth trading it in, not for me anyway. Someone even suggested it might be worth as little as £8K when I want to trade it in, and considering the car is all paid for, it is worth more to me than that £8K.