Please reallow uploading on Incubator because in some rare cases we might need to upload on Incubator itself.
So, please remove 'incubator' => false under $wgEnableUploads, and set the following under GroupOverrides:
'incubator' => array(
'bureaucrat' => array( 'upload' => true )
'*' => array( 'upload' => false )
'sysop' => array( 'upload' => false )
*Please* also resolve bug 10727, we are waiting on it for months...