Bill H. at GPA told me a while back that loos of magnetism led to a loss in the mid freq's., not the low end.
If I may chime in on recones, I had a 604c done by GPA a few years ago and with no disrespect the new suspension was very stiff, and whether or not related there was less bass than in an unreconed version I had around.
I ended up getting another original 604C and mended any tears and brittle areas of the cone with layers of tissue paper interspersed with and made rigid by diluted white glue, then painted. Doesn't look so slick but sounds a charm.