Which plug-ins did you install?
Some of the plug-ins from the Aperture menu - plug-ins link are outdated and do not work any longer with Aperture 3.4, see Aperture 3.4 and later: Some third-party plug-ins are no longer compatible
For example, the Maperture Pro plug-in cannot longer be registered, also the link to BorderFX leads to an outdated version, try http://www.iborderfx.com/BorderFX instead.
If you install successfully, the plug-ins should be installed in the system library in the folder
/Library/Application Support/Aperture/Plug-Ins , in subfolders "Edit" or "Export".
Once installed, you access them from the Photos-menu, "Edit with Plug-In" after selecting an image in the Browser.
I also have those plug-ins, and they should be installed in the system library in the following sub folders:
/Library/Application Support/Aperture/Plug-Ins/Digital Anarchy/ToonIt 2.6
Both appear in the "Photos" menu in Aperture, if I select an image, ctrl-click, and select "Edit with plug-in"