In older Topps sets, blank backs can be errors or proofs. Sometimes blank back proofs can be worth a lot, like the 67 Maris as a Yankee blank back proof or the 77 Jackson as an Oriole blank back proof, or the 84 Encased ( head all in the box), blank backed proofs, or the 85 Mini blank back proofs. In general, proof cards with some authenticity, say from Topps vault do bring a premium, as opposed to blank back errors, which normally do not
But agree with David and others that typically newer blank back cards, or wrong back cards, bring very little if any premiums, unless it is in an older set and involves a major star
