In the UK where I live, the S model has a certain rarity value because very few S models were actually sold here originally, most S models that are in the UK now have probably been re-imported from the USA, and some UK ones are probably fakes. As a result of that rarity, the S prices were slightly higher - for a while.
In the USA, where the S models were far more common, I doubt there would be all that much difference in the value compared to another model, as there were several thousand S models made originally.
Perhaps some of the forum's US members would care to comment on that, and correct me if I'm wrong?
The 750 'SS' models are quite rare, so I'd expect to pay more for one of those.