I would echo what the others posted. I had a non-S REx ('17 model) for 3 years and it was perfect. My *only* complaint about that car was the high beams. I live in a rural area and the pre-'18 refresh high beams were a JOKE. I replaced them with something brighter but they still sucked. And honestly, another i3 would never have been a consideration if they hadn't changed it. But they did, so when my old lease ended, I batted around a couple configuration options and realized that the aesthetics of the 's' were just so nice in red with black wheels. And the new high beams, HOLY COW, they're amazing!
Do I notice any difference in the driving characteristics though? Well, my old one had the sunroof and the new one doesn't. The carbon fiber roof if you don't get the sun roof looks really neat, so keep that in mind. That was actually a pleasant surprise when I took delivery. Sometimes I kind of miss the sun roof, but not enough to regret it, especially every time I see that cf roof in the sun. When I first started driving the 's', I thought I could notice a bit more pep but that's probably from less weight or just placebo. I did notice better handling feel in the curves, but it is slight. All i3's are pretty fun to drive in the curves.
Other than aesthetics, something you will get in the 's' that you won't in the non 's' is a sport mode. I hardly use it, sometimes forget it's there, but when I remember and the mood hits me and the conditions are right, it really does change the nature of the car! Not great to drive it that way in town as it's too jerky, but on a twisty country road like we have here, it's a blast.