The one advantage when booking a package with someone who is, or who uses, Walt Disney Travel Company (so...
disneyland.com, costco travel,
AAA, and I think getawaytoday.com, and maybe others) is that you get the little perks of the package.
With our costco package, we got vouchers for lanyards and pins for each of us, a 10% off merchandise coupon, vouchers for Mickey's ToonTown Morning Madness, Preferred Seating vouchers for 4 shows, a coupon for Marceline's Confectionery, and an almost overlooked coupon for some bus transportation over to a shopping mall. If those things sound like fun to you, figure out how much they might be worth, and then see if the price for a package makes sense.
Of course, it's possible to get some of those things from other people, whether it's through ebay or the sweet people here on the Dis who offer their unused ToonTown MMadness vouchers to those who might use them before they expire...but that's not a sure thing.
Look at all you get through a package, check out that package through other places (when I was booking our trip, after i delayed booking and saw a big price jump, the cost of booking with Costco, AAA, and disneyland.com were almost the same, with some factors being taken into consideration). Oh, and that parenthetical thought reminds me that if you're a member of Costco and use their travel service to get a package, they include a character breakfast, too. For me, when I booked, that was not free, as the package was almost exactly that cost OVER AAA and disneyland.com, but for others it has been less obviously charged for, LOL. It still worked for us, though.
Hope that helps!
But hey, if you do see a good price, JUMP on it. I delayed, and when I checked in the evening one day, the prices jumped up fairly significantly and so we paid hundreds more than we would have paid, if I had booked that particular morning. (and it jumped across the WDTC-using sites)