I've been meaning to do a full write up. I got the B12 kit with eibach springs, and decided to replace everything. Every mount, nut, washer. (Okay, missed 1 or 2 as BMW had a loooong backlog)
Kit I got here:
http://www.larkspeed.com/index.pl?a=i&p=9146181237&part=BMW-Z4-E85-2-2i-2-5i-2-5-si-3-0i-3-0-si-Bilstein-B12-Pro-Kit-Suspension-Kit
Then the multitude of BMW parts, and they really do add up. Top mounts front rear, spring cups, pads, bolts etc. Of course you don't need to swap everything, but at least this way its all done and all new so in the long run, will be trouble free.