It's a '72 Topps card so it's a very cool looking card format, one of the best in my view, it's Rose and it's in pristine condition so to me it has value. What the value is, I'm unsure, but there are Rose collectors, and a fairly large group of die hard Cincinnati Reds collectors so it should be desirable to one of these groups of people.
I think blank backs are generally less valuable than finished cards. I'm sure it depends on the card, but that's been my experience. Also, I guess you can consider an unfinished card a proof card and in this case a blank back. Who really knows whether Topps used it as a proof.
My guess... $100
Very nice card by the way.