I'd rather get a vet because I'm not comfortable with Rush or a rookie starting games yet and because I think Dak would play better with a distant but more viable threat behind him. Part of why he played so well in 2016 I think was probably having Romo on his *** if he made any missteps.
But getting that vet guy who's good enough is either very expensive, or you're getting a really old dude who's about to hang 'em up. Or you get a guy who just sucks all around like Weeden and Sanchez did.
Reading between the lines, it sounds like they might be looking for a QB3 in the late rounds of the draft to develop, as you suggest. I'd like a guy like an Orton, but not a drunk. Some dude who's got starts but isn't good enough to carry a team again and who appreciates that carrying a clipboard around is actually a pretty good gig for a couple of years. Experienced enough to help Dak on the sidelines and in the room, but to not threaten him all that much.