It would be superbly user friendly to be able to simply drag and drop document versions in the Document module. This would save you from clicking "Edit Properties" , searching for the file and pressing "Save".
Drag & Drop is over rated for uploading documents, particularity an individual document which would be the case here. You have to first minimize all windows, then resize the window containing the Documents module, then find the Document on your desktop or somewhere in your folder list, and drag it over. You also have to know how to do all of that. The current process would probably be quicker, but could be improved by placing a new 'Add New Version' button on the main Document page. This we will do.