advancedform 7.x-1.0

This has now been in use and tested on a number of live sites.

The 7.x-1.0 release adds a new PERMISSION that restricts access to the Advancedform toggle.
Add "Use Advancedform" as a permission in /admin/people/permissions

If a user does not have the permission, the advanced fields will still be hidden, but they will not have the ability to 'unhide' them with the on-screen toggle.
Again, this is not security, and can be thwarted by a client-side javascript hacker, but will reduce screen clutter without getting into full 'field permissions' etc.

If you need security, upgrade your requirements to use the field permissions module and use that instead.