This has been beat to death on here.
My personal opinions:
**Induction kit (Cold Air Intake, etc.) If you want more noise, great. If you want more performance, well, do you really think that the Mazda engineers, the ones that did the whole Skyactive thing would not be able to design an efficient air intake?
**Chips. On a normally aspirated SkyActive engine I doubt there is any real horse power to be had by tuning it or a "chip". It is a 13:1 compression ratio running unleaded fuel. In the UK, I believe it has a 14:1 and uses premium. You could remap the throttle response and make it *feel* sportier, but probably not really gain any power. On the turbo diesels, it can probably help.