Currently editing attachments requires that the user download an attachment, edit it, and re-upload it.

Products such as IBM's Quickplace, for example, allow the user to edit the attachment inline. Basically, that would:
1. Lock the attachment
2. Allow the user to launch the attachment (Word, Excel, Visio, etc.)
3. Edit the content in the respective tool
4. Save and close the attachment and return to the Wiki
5. Version the attachment after the Edit
6. Release the attachment

This will help a lot with complex spreadsheets which cannot be handled with wiki tables or large Word docs which cannot be posted as Wiki pages.