Ask questions, meet dancers, and be part of the conversation.
OP, I see where you are coming from.
I think the way I would put it is that the people who are most serious about their dancing ALL attend either USDSC or Ohio (and some do both, though that depends on pocketbook, not just seriousness). So while you do not have to qualify to be there--theoretically, it could be your first comp--you will be up against some of the best pro-ammers in the U.S.
I personally would have equal respect for a pro-am couple placing in the finals of USDSC or OSB, and that respect would have nothing to do with what label is slapped on the title. It's an impressive accomplishment to do that well at either of the two premier U.S. pro-am events.
I think the people who win it know what it has meant to them...and generally that has meant a helluvalotta work