Indeed I'm not sure if this specification was written with servers in mind. However, I do think that it would still be a good thing for Launchpadlib to have, and not only because it's used on desktop as well.
This blogpost has a good list of reasons: <http://ploum.frimouvy.org/?207-modify-your-application-to-use-xdg-folders>.
* a lot less cluttered $HOME (my mother will not cry anymore when the gtk file selector randomly choose to display hidden folders)
* Make backups a lot more safer and easier. (you know that backuping your $XDG_DATA_HOME along with your files is enough)
* A lot easier to reset a default configuration if you want/need it (and without any risk to loose informations). Even for the software itself could choose to reset $XDG_CONFIG_HOME if needed.
* Avoid some strange bugs that happens because you had a old version of some configuration file
* A lot more of flexibility and portability because no path are hardcoded. You use the XDG library that does the job for you. If you don't want the dependency, implementing the XDG specification is only a few lines of code.
Although the first reason probably doesn't apply to servers, the rest do.
Python-xdg is already a dependency of python-desktopcouch, bzr-svn and sinntp.