They are always going to be the new Matt Moore or Alex Tanney until they prove to be the next Tony Romo. The truth is we don't know who the player will develop into so you just go by whether they show the tools to try to develop.
I don't know what Vaughn's future is, and it's most likely with any UDFA QB that they will not turn out great, but I see a guy with the arm to play in this league, with the pocket awareness to play in this league, with the poise to play in this league, with the accuracy to play in this league, etc.
I'd much rather see Dallas try to develop that than go with Weeden simply because he was a high pick and has some experience. Those are the only things I've seen from Weeden that he has over Vaughn.