The IID isn't a scarce model, with over 20,000 made, but is an excellent shooter. It probably would be just an average seller on eBay, and, if so, not expecially valuable. Since it would probably bring in less than a similar condition Leica IIIa/c, I would be inclined to keep it. Lots depends on your own needs/wants, but it is a nice camera to own, and "better" than similar Barnacks, IMHO.
Harry