"These songs do belong to everyone now (so a levy would be wrong), but we only know about the vast majority of them because of the work of unpaid collectors who are often sitting on vast archives of recordings with no time or money to develop them (so a levy would be an excellent idea and fully justified)!
What does everyone else think?"
Personally, I think it's a brilliant idea, although how it could be set up is beyond my brain at present. I could see no problem with the equivalent of the contribution made for copyright songs being suitably allocated for traditional songs. If it was possible to say that there was only one place for the contribution for all trad. songs to go, it might be possible, but presumably any that have appeared in print have copyright on them, don't they, and the publishers/editors or whatever would claim copyright. It could get very complicated! And then, assuming that this could be sorted, there's the subsequent distribution of the fees... Maybe the National Sound Archive could (but would they be prepared to?) handle it, but to whom would they distribute the money?