My front and rear sway bars to the mazda speed 1's. Do i have to upgrade the strut tower brace.

If the sway bars improve less body roll from left to right. Does it also fix nose dive?

What does the strut towers do then. do those just help over all left body roll.

And what will correct for less nose dive.

anytime you increase suspension stiffness, you increase load to the chassis, so yeah you should upgrade the bar. it wont be a night/day difference, but not a bad idea. check my thread on strut bars in the wheel/tire forum before you buy. it wont do anything for nose dive, they only resists one side moving in the opposite direction as the other (body roll). only stiffer front springs will do that.