Wheels & Tires:
Wheels can definitely be bling. The point here is to upgrade and gain more benefit from a larger wheel.
If you go from a 16" to a 17" wheel, the tire's size will have to change to maintain the same overall diameter. What this does is it effectively keeps the speedometer reading the same plus it virtually eliminates any possiblity of interference with the suspension or body.
A smaller sidewall on a 17" tire is stiffer than a taller sidewall on the 16" tire. The problem comes in when you go to a 17" wheel/tire combo from a previous 16" set-up, but the suspension is the same. Now the 17" tires are doing more work and the suspension has a harder time keeping up.
The opposite is true when say one beefs up the suspension, but does not upgrade the tire or tire/wheel combo to compensate.
In short, an upgrade to a 17" wheel/tire combo can be beneficial with respect to handling.
Better pads can do a better job in stopping the car.
Repeated braking (i.e. as in racing) are better handled by better pads and/or better rotors (slotted; cross-drilled; or a combination of the two). The better pads can handle more brake fade. The better rotors handle more heat dissipation.
Larger rotors and matching pads (and of course, bigger calipers) will do a better job because they have more braking surface area to do the job and bigger brakes overall will contribute to better heat dissipation and thus less of a chance for brake fade.
If again you're doing moto-x, track, etc. then a step up from stock pads may be in order and/or better rotors (slotted; cross-drilled; or a combination of the two).
Changing the brake fluid to one that has a higher boiling point and/or is for street/track will also contribute to better braking.
Changing the brake hoses to stainless steel braided reinforced lines will also help. These do so by eliminating some of the flex in the hose that occurs as a result of the braking action. Less flex means more stopping power to the calipers.
In addition, a better tire will also aide in stopping a car, whether it's a better tire overall (construction / purpose) and/or a wider tire for more surface area to contact the road -- but you can only go so wide before you have interference with the suspension and/or body.