Secondly, does anyone know of a method to track down unused variables in large perl scripts, without the manual rigmarole?

I think the Name "%s::%s" used only once: possible typo warning will do what you want (see perldiag for caveats). You are using warnings, aren't you? ;-)

Otherwise, maybe there is something in either Quickly detecting variable writes or in diotalevi's Devel::Spy that could suit your needs. If you figure something out, please post your solution.