I think that the S970 has 8 more Mega!Voices but they're all guitars, basses, and strings. No new category of Mega! Voice. So the styles should sound fine on the S950. Many of them will sound a little better on the S970 because of the Real Brushes and because of some additional DSPs.

The dance styles might be another story. I don't play them, but I notice that there are many new synth sounds on the S970.