Definitely worth it at used c.$650. I bought one at that price to use with my PS Audio Lambda/UltraLink combo, and it much improved the sound: in particular, reducing the amoung of digital 'glare' and better separation of orchestral instruments. I didn't notice any reduction in bass response. One caveat: use really good interconnects, such as the Kimber D-60, or you won't get the improvements.
