I confess to being a little lost in the large amount of detail in the replies to Bookworms question.
From the light aviation standpoint, where most airplanes do not have an FMS, so cannot give the added information, and are probably only on flight planned routes for a small percentage of their flying, the main advantage of equipping light airplanes with Mode S appears to be in avoiding TCAS uncertanties.
Bookworm, when you have absorbed all the information, could you post your conclusions as you seem to have a greater understanding of the salient points than do I. Thanks.