I've got a 2015 S Premium, and I'm very happy with it. Perhaps a bit late to the thread, but let me add a bit of my own perspective to the discussion:
You bet, I want the more bolstered "sports" seats, the rear disc brakes, the fog lights, the turn signals on the mirrors, the improved instrument panel, and so on that you get with an S. With the Premium, I also got navigation, moonroof, Sirius/XM radio, Softex seats with a powered driver seat, etc. With seat heaters that are the most effective seat heaters I've ever experienced in any car at any price. You only live once -- you might as well have the creature comforts that make driving a pleasure.
I'm very happy with the Softex seats -- "better than leather," as far as I'm concerned. Instead of goopy leather care stuff, I use the same interior cleaner I use on the dashboard, and it does a fine job. Also, a powered driver seat is a "must" for me -- driver seat comfort is absolutely my Number One requirement. I'm nearly 60 years old -- once you young guys get to be my age, you'll probably appreciate seat comfort a bit more than you might now.
"Sluggish" is not any problem with an S model -- just press the "Sport" button if you need faster response, and you'll get it. It makes a big difference. Technically, the steering, the throttle, and the CVT are "electronically programmed," and putting the car into "Sport" mode changes the shift points and the accelerator response, and tightens up the steering feel -- using a different "program." Otherwise, the CVT is indeed programmed for less performance and better fuel economy, which is what I want most of the time.
In the end, I find the driver seat to be among the most comfortable seats I've ever owned, and the low-profile tires aren't too bad, providing quite a bit of handling without compromising ride quality much. I'll definitely replace the OEM tires with "touring" tires when they wear out, to get perhaps a bit less handling and definitely more comfort, but the only complaint I've got is when going over really rough pavement, like old concrete where the smooth top surface has worn away -- that's when the OEM tires are at their worst.
I'm always a bit amazed with the posts in this forum about "adding navigation" or fog lights or other features that people didn't get with lesser models -- it's definitely a whole heck of a lot easier to just get them as standard equipment or options in the higher-level models when you purchase the car. I suppose that, in the grand scheme of things, there aren't a whole lot of people who want "stripper" cars, so if you buy a higher-level model, you should easily get the money back for the higher level models when you sell the car some day.
Finally, regarding gas mileage, I'm getting a bit over 35 MPG on average, and I've gotten several tanks on the open road at well over 40 MPG. And that's actually doing the math, instead of relying on what the onboard MPG display says. I rarely put more than 10 gallons in the tank to fill it back up, and that's definitely part of why I bought a Corolla -- to get excellent gas mileage. In summary, I'm very happy with my Corolla S Premium, and I'm very glad that I went for such a top-of-the-line model. It has the creature comforts that I use and enjoy every mile I drive it.