Enable linking to attachments in different spaces and pages using the "link" icon in Editor toolbar.
Presently, an user can use the Insert/Edit link to link to attachments attached to the current page only.
Please see associated discussion here:
"Unfortunately, I'm in a situation where most of our users will simply not refer to the attachment at all rather than learn the notation for adding the attachment in wiki; in other words, if they can't do it in the GUI, they won't do it at all."
"What I'd like is when I do a search, or i go to the Recently modified tab, that attachments also show up, regardless of space or parent. "