Maybe I'm a bit out of touch in regards to how the legality of MP3s is at the moment, but would whatever music I ripped from my CDs suddenly become illegal or illegitimate if I sell off said CDs?
I believe that to answer that question, you need to hire a lawyer.
As a lawyer, but not one in this speciality at all and having no knowledge or experience about the matter, I would say that you have probably lost the right to listen to that music. I believe that the principles of property law and intellectual property law would back me up on this.
The real question, I think, is who will enforce it. Who will spend the money and time to determine whether all of us have the real legal rights to all of the music that we claim that we do. That would be an administrative nightmare to achieve regulation on that matter. So... not as your attorney, I would say don't throw anything away that you've got. As an attorney (not yours because you haven't paid
) don't buy new CDs then go back and sell them away after you've ripped them and gotten the advantage of iCloud.