the variable list is a well known feature when debugging.
The "hide empty superglobal variables" filter works as defined in many cases.
Look at the drupal function "theme_render_template()" on this page:
The function extracts an array to local variables and than includes a template file.
In this template file all extracted variables are available but are not visible in the variable list. ...well, not until they are used at least one time.
(BTW: global variables are listed, such as $_GET,...)
I think you see my point: if you don't see a variable in that list you don't know it exists...
Is there a setting I don't know?
There is an equal issu (http://devnet.jetbrains.com/message/5447235) regarding code completion and I understand the performance thing, but in this case it should be different, right?