There are certainly a lot of advanages NXT brings as far as branding the talent before they enter the main roster. But I think that's the icing on the cake more than the actual cake. They wouldn't be spending the money they do on NXT if they didn't legitimately feel it was necessary for helping build the companys future.
But that comes at a price. A big one apparently. Still I'm sure Vince see's it as an investgment in the future. He'll get his money back with the Charlottes and the Roman Reigns of the future, hopefully.