Sometimes they will offer special incentives for booking through them. Beverage mugs, rebates, etc. I really don't know if they have any right now or not.
I'm not surprised that there is nothing out there different than booking through WDW right now. With the new packages, Disney feels they are giving you the best price they can.
I did find one loop-hole however...We really don't need MYW passes, but wanted to get the dining plan, so I entered the dates, selected a 1 day MYW pass, and could add the dining for all of the nights of our package. It seems silly for us to pay for the passes, but there is just 1 adult, and 1 child and we really will save a ton on food using the dining.