The hicolor theme seems to be part of the gnome-media extension. Not sure if it should be there or it's own extension as it is a source unto itself. Either way, that index file should be created and place in the extension that contains the hicolor icons, using the gtk-update-icon-cache command.
EDIT: It seems only the relevant icons from gnome-media are in the hicolor directory. Perhaps a hicolor icon extension will fix the issue.
The hicolor icon theme itself is a placeholder for the default fallback theme, filled by applications like gnome-media and others. I will submit it shortly as an independent extension, which also contains the index file. It will solve the problem.
Regarding missing .gtkrc-2.0 default can go to the gnome-icon-theme extension as it refers to it. Normally it is not edited manually but by gtk theme changer programs. As it is in the home directory, changes saved automatically with backup. Backup is restored after extensions loaded and startup scripts executed, default value will be overwritten from backup so no any harm to have it.
As an icon theme changer,
lxappearance works fine. It is desktop independent, no need LXDE to use.