plz be aware.. speed 3 springs on mazda 3 will actually raise your front by about 1/4-1/2".. since speed 3 is heavier in the front, springs are stiffer. They do increase performance, just dont look as good.
if you want to go with tein springs, I personally have s techs on my car, shocks/struts are holding up for a while now, without major problems. They are too soft for me so i went ahead and ordered BC coilovers.
And no, you dont have to change your shocks/struts but u can.