They need to look at resale, legacy etc of ebooks such as Kindle.
Yes, that is potentially a much more lucrative field. I'd be much more likely to let go of an eBook, once read, than any digital music files.
I think it will be tough for ReDigi to convince the courts that this isn't just a way of monetising illegal file sharing. They admit to no good way of being able to verify that a "seller" has deleted all copies of the file they have sold. They talk of some spyware type of thing that would search sellers' computer for residual copies on an ongoing basis, but really, that sounds absurd.
No, the cat's out of the bag on duplication and distribution of digital music. Whilst I still buy all my stuff, and legal downloads are about to surpass CD and vinyl sales in the US, to the younger generation, the idea of paying for music just seems ridiculous. Artists and record companies are soon going to (already?) need a very different business model.