Listing variable values using drush
If you do 

drush vget theme_THEMENAME_settings


it will give you all nested variables but nested variables  don't work

drush vget theme_THEMENAME_settings.toggle_name 
drush vget theme_THEMENAME_settings:toggle_name 


so the only way I found to get nested variables is with the use of grep

so for my theme I would do something like this

drush vget theme_THEMENAME_settings | grep toggle_name:


or do further processing using cut to get just the value of this variable

drush vget theme_THEMENAME_settings | grep toggle_name: | cut -f2- -d:


where theme_THEMENAME_settings is my variable and toggle_name is the nested variable name