In '98, I auditioned well over 10 speakers in the 3-4k range, and did some traveling to accomplish this. This included Avalon and Dunlavy, which were a bit more expensive than the Thiel 2.3. At the end of the experience, the Thiel was the obvious choice for me. No other speaker could handle complex and congested music as well.
Yes, the bass doesn't go down very far, but what bass it did have was very clean and articulate. Sure, the double basses, kettle drums, and gongs were not as full, but everything else was there. Also, there is also an inherent brightness that needs proper cable and component matching.
Is the Thiel 2.3 for everyone? Hell no. But there are very few speakers that can play to the Thiel's strengths at their price range. All speakers have inherent downfalls. I suspect David99 understands these things because he has decided to stay with the same brand.
As far as getting a used 2.3, I think the prices on audiogon are too much. This is a speaker that sold in '98 for $3000 and has essentially been upgraded twice. If you heard the 2.4 and really like it, then get this one. Better yet, look for a demo pair 2.4 from a dealer. Also, try to have a listen to the 6, because this will give you better bass and there have been numerous 6s on the market.
Rob