One thing that might help is the solution here (Content that is a Collection): Creating a NodeType that is Content and ContentCollection . That way you avoid the confusion between selecting the collection and the content node.
Another Problem is allow direct selection of the item and not the content inside. I dont know wether this is a problem in your case. A possible solution therefore would be to render some info-text before the content (only in backend) to give the editors something to click to.