If you are going to throw parts at the front. Here's a thread I did on it.
The Complete SPL Front Suspension
Since you said that you have 80,000 miles on the Z. If you are going to replace the lower ball joint, it comes with the lower arm and bushings. If the lower bushings was bad. I think you would know it. The rear is a big silicone fill donut. Just like the diff bushing that leaks.
I would check the sway bar end links to see if there is any looseness or play. Mine will squeak after they get wet, then dry out.
The dead spot you are feeling could be from loose tie-rod ends, OR the rack itself. Check the ends first. If they are tight. Then it's the rack.