That's a tough and kind of impossible question to answer, because just like marginal differences in audio are worth different amounts of money to people, money itself is worth different amounts to people.
To my ears there is a very clear, audible difference between the LCD2 and LCD3. I picked up the LCD3 at THE show in Newport last year, listened to it for 2 minutes w/ the CEntrance Dacport w/ spotify and instantly knew it was substantially better than the LCD2 and I wanted it. Since then I have tried the two headphones w/ my iphone, Xm6, Schiit Lyr, Meier Concerto, or Schiit Mjolnir and in each instance I heard audible improvements immediately. I do see the gap widening as I moved up in amps, where imo if one was buying an amp >500 I would consider buying the LCD3. It was really the Lyr that drew the line for me where amps that were better than it really made the LCD3 "$1000" better than the LCD2. For example I would much rather have the LCD3 w/ Mjolnir than LCD2 w/ WA22 or GSX and I would rather have the LCD2 w/ Mjolnir than the LCD3 w/ lyr.
^ Agreed (except for the LCD-3/Lyr combination...found that one pretty lacking).