It's the cumulative effect of all the upgrades that put the 2017 significantly ahead:
- It's going to be a bit quieter at cruising speed with the new insulator mats.
- The reviews have made it clear that it handles a little better, with sharper turn-in and an increased capacity for dispatching rough road surfaces (e.g. track curbs) without being thrown off-stride.
- The revised VSC with its new Track mode brings more flexibility to the stability control system, providing more graduated intervention, and so permitting more "natural" tail-out fun while still maintaining a safety margin.
- The new digital readout functionality is a nice bonus, and to my eye it looks OK - not up to Porsche standards but this is a sub-$30k car
- The styling changes and interior trim changes (like the new IP in the Limited) while not major collectively work to improve the look of the car.
- The head unit/display is now mediocre rather than awful.
- The PP offers Brembos with better brake feel and more fade resistance as well as upgraded dampers which should improve the ride and handling to some degree.
- There is some amelioration of the torque dip, and a slight enhancement of the overall torque curve.
- The engine and chassis have both received some refinement and strengthening upgrades which should bode well for improved reliability and improved capacity to handle mods.
There are probably a few other changes I have overlooked here - like the improved lighting system and the steering wheel controls.
Again, no one of these makes a big difference on its own, it's their collective impact on the car's overall quality that makes the 2017 the smart choice for current buyers.