You only have a closing when they are deeding a new property to you. Resale is buying a piece of a new room (new property) but adding on with Disney is just buying a larger percentage of the room you already own so no closing just new doc fees. You can negotiate the closing costs, for example i would pay the asking price and have the owner pay the closing and maintenance so the cost per point is high and in turn you have a lower chance of Disney ROFR'ing it but you will brake even in the final cost.
ROFR - right of first refusal - if the selling price per point is too low Disney will just step in and buy it themselves.