I don't see how steering wander is caused by worn struts??
and wouldn't worn swaybar bushings cause wheel hop??
again, not steering.
Bumpsteer is a different issue, and is worsened when a car is lowered - that's true.
I also wouldn't recommend going more than 1.5 inches unless you want your car to ride like a tank since the suspension will be about bottomed out in the rear. A rough ride
you were asking about is from the stock axle pinion being in a foreward angle, and when it's lowered the axle is close to the snub and bottoms out in the rear. The front rides rough because the A arms are on an upward angle and have limited range of motion.
Slammed looks cool, but the mustang suspension cannot ride good in that position.
This also doesn't address 4-link bind.
Bump steer can also occur when car's are lowered because the a-arm isn't paralell with the tie rod, then when the suspension travels it pulls the camber of the wheel in and out. this will cause the steering to wander when you go through dips and stuff.
If you have any other quesions, feel free to ask