An import/export facility for the blacklist and whitelist would be useful. I admin many Joomla sites and would like an easy way to propagate the IPs to all sites. If they are blacklisted on one, it's almost certain you don't want them on any site.
Perhaps this could be managed through a central list in SP Control Centre...?
This is important for individual IPs rather than global. Global blocks tend to be site-specific.
No, currently there is no way. Exporting and importing configuration will overwrite all settings...
I'm currently working and there will be an option to export and import blacklist/whitelist IPs in the next version