I keep reading about revised/unrevised z springs. What is the main difference between them? I'm in the process of lowering my sedan and want to see I this is a good and cheap route to go. I did search and couldn't find any anwer. Thx for any info.

You didn't search very well then because its reposted almost every week, but the differences are that in 04.5, nissan revised the rear springs on the 350z, so the springrates went from 342 to 427, thats the difference in springs. The shocks were also changed in the rear.