Buy a $40,000 used DAC for $4,000 or a new one for the same amount?

The advancements in DAC technology make them one of this hobby's most perishable products. But ... what if you can buy a 10 year old DAC for $4,000 that initially cost $40,000? Is it a bargain or waste of money compared to a new DAC that is $4,000? I understand it depends on the specific model etc. But in general, has the technology gotten that much better? And how quickly will the new DAC become outdated? Is it like computers? Past their prime about 3-4 years so you plan to replace them regularly? Thanks for all comments