Ahudson's 3D Content Installer is capable of installing mass zips into Poser runtimes given that you manually point it into those directions. 

http://www.renderosity.com/mod/bcs/index.php?ViewProduct=61876

Of course, there are limitations.  It will analyze each compressed file for proper library structure or else it will not install the content.  It will delete compressed files after installation unless specifically told not to.

Personally, I think you should rethink what content you should to reinstall.  I am sure that most of the files you load into Poser do not get used more than once or twice.  It is just a waste of hard drive resource.  But if you are hard pressed to let go, next time you upgrade, just add the previous version's runtime to current as an external runtime.  In that order, if you feel the need to go backwards, you won't need to reinstall content again.