Monsta,
they didn't yet have the s when i bought mine last year. you can find more forum chatter on these bikes at multistrada.net. they're mostly brits and assorted euros (so you'll feel at home...just kidding), but they know a lot about their bikes and from what i can gather the s is only marginally better than the base bike.
I don't think the extra money is too much for the s, especially when you look at comparable bikes like bmw's. I did not see another multistrada in the rockies despite passing thousands of other bikes. I did see a ton of bmw's & a few other ducs. Mine is very nimble and extremely torquey. It's like putting street tires on my crf450.