It depends on your dish angle as to whether you will need that longer mast that came with the Dish1000 or not. In a lot of markets the longer mast is not needed.
I think the biggest reason for the longer mast with the D1000 is to clear any problems with the roof if you mount the mast to the eave instead of the rooftop.
Me, I'll use what's already there (even a D* mast) as long as I've got clearance. Doesn't hurt to save a few of the longer D1000 arms for that rainy day.