Check what the close focus distance is. I believe that most were about 11 feet or so, making it a bit impractical for family photos.
Also, the design is a Tessar derivative, rather than based on the Carl Zeiss Sonnar, which most other lens makers copied. Add in the fact that it was a bit slow at f/4.0. By 1968, many lens makers were shifting to f/2.8 Sonnar derivatives.
Lenses for the Retina IIIS were interchangeable with the Retina Reflex S, III and IV, as well as the Retina Instamatic model. I think the 200mm lens for the Reflex cameras won't work with the Retina IIIS.
Sorry this was so lengthy. Value is always difficult to estimate, but I would guess it to be $50-$75, give or take $25.