Have you booked directly with Disney? If so, you can contact them about the cost of an upgrade, otherwise you will have to go through the agent you've booked with. You can't contact AKL itself, you'd need to go through WDW reservations.
It's probably worth waiting until you check-in to enquire about the cost of an upgrade. When we were there in 2001, we asked about upgrading from our savannah view to Concierge and managed to get it for £20 per night (and that was for the room, not per person).
If you can get the upgrade for a reasonable price, then it's definitely worth it. Otherwise, it probably depends on how much use you think you can make of the food and beverage offerings. Due to its location, AKL isn't really a resort you can pop back to midday and if you'll be eating out in the evenings, you'll only really benefit from the breakfast offerings. The Sunrise/Sunset Safaris are only available to Concierge guests, so if that's something you're keen to try, it might be worthwhile upgrading.
