I would definitely pay the extra $10 only because we went there last year and were put in the Country building! We had requested Jazz and knew this wasn't a guarantee but hadn't planned on being put way back there. The mornings weren't bad, the walk was pleasant, but at night, coming back from the parks was horrible! We'd be so tired, it seemed like it took forever, especially with a four year old. We didn't have our own stroller, we rented them and it was not fun carrying a sleeping child all that way either. We said if we ever go back there again, we'd definitely get into the Calypso building.
Hope you enjoy your stay at ASMU, we really loved it there (except for our location!) and I always recommend it to families as a great place to stay while at WDW.