The only thing that hurts the value is that the new 686's are also round butt, someone who really wants one can just get a new 4" 686 or have a used 586 "round-butted" by a skilled revolversmith. I know Pinnacle will convert a square to a round butt for $95.00, so if someone wasn't interested in a collectible, a decent used 4" 586 for around $500 + about $100 for the work can put you in at $600 ballpark for a round butt 586.