In the 50 or so seasons that I've played since they instituted DiTRs, I've probably had about 75, 1.5 a season on average. Of those about half a dozen became MLB quality players. IIRC, every DiTR that I ever cared about was either a catcher or a reliever - my impression is that since they tend to have the lowest OVRs they tend to make better DiTR candidates.