Check the General Public Discounts at Mouse Savers....
The "emptiest" resorts will probably be the ones that are most heavily discounted.
Example: "Summer Savings Offer"
Value Resorts: get up to 15% off, except:
Art of Animation Family Suites: get up to 10% off
Moderate Resorts: get up to 20% off
Deluxe and Deluxe Villa Resorts: get up to 30% off, except:
Animal Kingdom Lodge Savannah View & Club Level, Beach Club Resort, Contemporary Resort: up to 20% off
Animal Kingdom Villas, Beach Club Villas, Villas at Wilderness Lodge: up to 20% off
Reading this backwards - the Values are doing fairly well, Moderates in a LITTLE trouble, Deluxes BAD, except for Beach Club Resort, Contemporary Resort, Animal Kingdom Villas, Beach Club Villas, Villas at Wilderness Lodge.
This sort of follows our observations from our April-May 2014 trip.... WDW is having trouble filling the Deluxe Resorts at current "rack" pricing. We're hearing from a number of our wait staff friends that the RESTAURANTS are pretty busy - but that HOTELS aren't very full.