I wonder if you guys have ever considered asking archive.org to host your files?
The Internet Archive is now recognised as a library in the US state of California, and it specialises in archiving public domain material.
The one problem with the IA is that it is not very easy to search, so some collaborators maintain external indexes (eg http://www.raretunes.org), so this site would still be very much needed, but any problems of bandwidth would be alleviated, and it would provide more backups in case of data loss. Furthermore, any donations made to archive can be tagged with your own text, including the site URL, so you may even increase your visitor numbers while reducing bandwidth requirements.