Q. I already have the oik base plugin. Do I need oik-lib as well?
A. No not really, not at the moment.
Using oik-lib may reduce the need to deactivate plugins when performing updates to plugins that deliver functions upon which other plugins are dependent.
In the future you may decide that you don’t need the oik base plugin, but do want to use other libraries. In which case you can switch to using oik-lib and other plugins that provide shared libraries following the oik-lib API.