My theory for buying a used piece of gear is that someone else is taking the largest part of diminishing returns. For example, a Rega Planet, if someone who bought it new for $800 sells it a couple years later, they'll get $400. If I buy it at $400 and sell it a couple years later, I can probably still get $250 or $300.
So, it seems to me that a NEW CD player has more diminishing returns than a USED one. This leads me to believe that the best CD player for the money will definitely be a USED player.
