Have just heard of a scheme in the States, run/set up by Sony, which takes in your old ereader in part exchange for your new device.
Apparently, you used to be able to trade in any make of older reader, but now changed to Sony products only.
It's called EcoTrade, and while not a massive amount (around $20 I think, although at one time it was $50, against a US price of $129 ( I know, no fair, no fair ...... )
What a good idea ....... unless of course, you can't bear to part with "obsolete" technology ........