I've got two Z570SS' and its worth it. My wife's SS quit working and it automatically went to "soft" mode, which gives her a smooth ride, but it bottoms out in the rough stuff. By this it's very easy for me to jump from mine to hers to see the difference. I'm going to look at her sled this week to see if a wire came off or something. Beyond that my dealer said bring it in. It's the only failure he's seen so far.
For $500 get one. There're gone on the 570 for 2003.