If you think of the directory as being a file that contains the file name and the inode number, then when a file is removed or unlinked the size of the directory isn't reduced so there is a possibility of performance degradation due to the sequencial search for a file in the directory.

The way to fix this is to cleanup the directory and then rename it and then recreate the directory.

e.g.

cd /var/spool/mqeueue
mv mqueue old.mqueue
mkdir mqueue
chown xxx:xxx mqueue
chmod xxx mqueue
rm -rf old.mqueue
[download]

Get whatever you need from the old.mqueue directory before removing it, obviously.