I jumped from the Insight to the 20/20 with LPS. After selling my Insight, the 20/20 cost me about $550. Once broken in, the improvement was significant. I found that lower mids and bass had more authority and weight. Really great for piano, percussion and, obviously, bass. The toe-tap factor is exponentially higher. I noticed less of a change in the upper mids and treble. Adding the LPS to the mix equals better dynamics, a more solid image, and a better sense of depth.
Granted I got an amazing deal, but I've been very happy with the improvement. Would the Duo be an even bigger improvement? Probably, but it's outside the price range I could justify for a phono pre.