To compete at club level or the top international level a one-way will definetely give you an advantage on a sweeping track. A one way keeps the front wheels moving all of the time, even off-power, this will give you better corner speed at the expense of having no useable breaks.
Sway bars are a fine tuning option. Basically it's like having stiffer springs but only when you are cornering so your car will soak up the bumbs on the straight but not lean too much in the corners.
These 'tuning aids' will only make a difference only when the track is suited to them - knowing when to use them, and good driving ability is the way to get that advantage.