Thanks to everyone for their input on this. We are in the process of adding an extra option to the item settings menu that will allow you to download all attachments within that item.
The way it works is the same as the project-level download button – it will collate the files in the background and email a link to you.
Our asset management will be undergoing a huge overhaul that will simplify this process even further, but until then we hope you find this update helpful. As always get in touch with any feedback through the usual channels.