Somehow, MacPorts does not seem to update the GNU texinfo dir file contained in /opt/local/share/info. But there is a nice script available in the ctan, which generates a new dir file. You can download it here.
I like to use MacPorts for installing certain libraries and programs. When running an update old versions are still kept on your disk. I never did care for those old versions, so you can simply let MacPorts remove them while updating:
$ sudo port -u upgrade outdated
This is taken from another blog post.