hook_menu_alter for taxonomy vocabulary
The code looks good! However, try the following:


See if there is already a permission or a module which lets you control the things you wish to control. Maybe you can mention the desired outcome or the objective in the question?
Add a dpm() or something to the end of the function to see if the $items are being modified correctly.
Add a dpm() or something in the _term_account() function to see if it is being called correctly and that it is returning TRUE or FALSE correctly as per your requirements.