I sometimes book a package through Costco if the price is better (this information is based strictly on staying on site, though). For instance, if I get a dining credit for character meals for each person plus a gift card (which is what Costco often offers), it's sometimes a better deal than booking it all separately. Since I have an AP, I call and ask them to leave the ticket cost off of mine and they do that. When I'm there with my family of 5, and let's say we get a $55 premium character meal voucher per person, we use those for regular dining so it's $275 toward food. We usually get something like a $20 or $40 gift card as part of the package as well.
Often, though, even factoring in the above perks, it's still more expensive to go with a package. I usually go to DL when there is a significant hotel discount so it's rarely better to go with a Costco package in that situation. I tend to get AP deals, go during mini Gay Days or Dapper Days which saves 20-50% on the hotel.