Currently, if there is a link to a page in another space a user doesn't have access too, the link shows up in red highlighed text. My suggestion is to have the red highlighted text link to a customizable "You don't have access to this page" page. This would serve several purposes:

• letting the user know what the red highlighting means - that the page exists, but they just don't have access
• the page could provide a way for the user to request access to that page/space through either an email link to the conf. admin or by a web form

This functionality could be further enhanced by allowing pages that the user doesn't have access to, to show up in searches (but only show page title, not content). This would let the user know that the content exists in a space somewhere, they just don't have access to it. And again, by providing the customized error page, the user can request access and if appropriate, the admin can grant access.