It's more of a "let's celebrate being the last car sold in first world nations to get Apple Carplay" refresh, which I think is pretty big actually. A new touchscreen that mitigates the Achilles' heel infotainment is big too. The fact that the current top powertrain is slower than the German 4 poppers isn't that important IMO. People buy this for the reliability rep and the Japanese-ness.
The IS will continue to be a solid used car, but this update may improve its appeal as a new car too.