I lowered my 280Z a year ago using suspension techniques 280 lowering springs, tokico cartridges, and msa bumpsteer spacers. I also took that opportunity to replace the ball joints, tie rod ends, and a the sway bar bushings, as well as do a little cleanup. This lowered the front and rear about 1.5".
Some pics of that swap in this album: http://www.imagestation.com/album/pictures.html?id=2122587659
JCWhitney.com was selling these springs for around $150 a little while back. I paid over $200 for mine when I bought them. I can only speak for the Suspension Techniques springs. I've seen msa and tokico springs installed and thought these gave a better overall stance. I have them on my 240 and my 280.
The hat swap is only for the rear, as the front hats can replace the taller rear hats if you have a spare set. This takes off about an inch, if i recall correctly.
I've done this swap several times on Z's and can help out if you need. I can get a spring compressor, too.