Since a user's .gtkrc-2.0 will overwrite any settings specified in the user interface settings (and I've seen countless users run up against this), it'd be nice if the user was warned about this. Obviously you could get fancy and check exactly what settings are in the gtkrc and disable those options in the UI dialog, but I imagine it'd be sufficient to just pop-up a message when the UI dialog loads stating that this file can overwrite xfce's settings.
As someone mentioned on IRC, a dialog could get irritating since there are legitimate reasons for using a gtkrc that won't override your xfce settings. Maybe putting a label in the dialog as a warning would be a better idea (similar to when you run thunar as root).
Close bugs in products that are not active anymore.