You can apply ACLs to the assets node to restrict what users should see it. For example if you look at the node /libs/cq/core/content/nav/sites (in AEM 6.0) you will see there is a ACL that denies dam-users and mp-contributors. You could so something similar for the nodes that you're interested in. If I recall for AEM 5.6.1 the nodes might be under /libs/cq/gui/content/common/links, but the same concepts apply.