It would be super useful to be able to add tags to attachments, and to be able to view attachments independently of the tasks to which they are attached (making file/document management easier).
Our use case is when spaces are for an instance of a project or event that is repeatable (e.g. annual conference). Managing attachments by task means they disappear from easy view as tasks are completed. If we can see them all in one place with tags, it's easier to find key documents from year to year (or even within a year for that matter).