That is not a terrible price for used CS3.6's, if they are in good shape. I own a pair myself, and I do not feel that they are outdated at all. These are very flat speakers (29Hz-20kHz +/- 1.5 dB), and are rated down to 27 Hz. So yes, their low end capabilities are impressive. By comparison to the newer Thiel models (CS1.6 and CS2.4), they are more full, but perhaps not as "sharp" sounding. However, I prefer them to the 2.4's, myself. Also, it is somewhat telling that we have not seen a CS3.7 yet. Thiel does not put out a new model unless it believes that it can present a significant upgrade over the previous model. So that tells you that they have had a hard time making the 3.6 significantly better.
Hope this helps, Tom.