Netbeans 6.7 does has this feature: Importing Plugins From Previous Release Into The New One, but it seems a bit shy about it.
When the new version of Netbeans is launched you'll be asked if you want to import settings from a previous version.
Click yes and Netbeans will look for compatible plugins in the background.
Note that you won't be prompted again. Instead, after a few minutes, an icon should appear in the bottom-right corner:
http://lh6.ggpht.com/_BEizchvf9zs/Sk83UjMwZBI/AAAAAAAAABQ/hlX5DT-k0fg/s800/netbeans-screenshot.png
Not exactly in your face, right?
Click on that and you'll get the option of installing any compatible plugins.
Also note that if you exit this process at any point then the icon will disappear - restarting Netbeans will bring it back (though you might have to wait for it to do another background scan).
Finally, you can also trigger this process (and choose an arbitrary userdir location to import from) with the command line option -J-Dplugin.manager.import.from=/path/to/userdir
e.g. in Vista:
C:\Users\JDoe>"c:\Program Files (x86)\NetBeans 6.7\bin\netbeans" -J-Dplugin.manager.import.from="C:\Users\JDoe\.netbeans\6.5"
or in Ubuntu:
/bin/sh ~/netbeans-6.7/bin/netbeans -J-Dplugin.manager.import.from="/homes/YOURHOMEDIR/.netbeans/6.5"
This might be useful if you want to import from a beta install.