I replaced mine with urethane ones from fulcrum suspension as my old ones were shagged (drivers side came out in 3 pieces)
Its a simple job to do, and im glad i did it.
There is no increase in NVH at all, and turning seems a little crisper.
I undid the top bracket that secures the rack to the x member, then manuverd the rack up a little (didnt have to disconnect any ps lines) and just slid the old ones out. The new ones from fulcrum had a slit in them same as std, so i just slid them in, and replaced the tops on.
i was doing tie rod ends at the same time, so it made it a bit easier too...