S23--
Have you HEARD a CDS2 or CDS3 against Wadia. Levinson, Meridian, etc.? I have, and the Naim players devastate the Wadias, Levinsons, etc. I once heard a Naim CD2 vs. a Levinson 39 in an Ayre/Avalon system. The Naim was much more dynamic and muscular, with much better bass control and extension--it was much more "tuneful." The Levinson, for its part, was slightly smoother, was more detailed, and did the imaging/soundstaging thing a bit better.
And when I heard the CDS2 against the Wadia 861, it was not close--the Naim player just walked it, as it did against the dCS stack.
As far as older players go, get the serial number and see if it has ever been serviced--you can email Naim or Naim Audio North America. The best service department I've never used!
Best,
Bob