I hate to say this, but the official "save as" dialog do have one (huge) advantage; the sketch name is pre-filled, and it's very easy to just change it a bit to save a new version. For me that's really more important, and the GUI open button works really well for opening sketches (especially after finding out I can sort sketches in sub-folders and they will appear as sub-menus).
But still very nice work! I don't know how you do it. I will definitely keep an eye on it in case you improve it!