How would you find them otherwise ?
If there was a searchable member list, and you didn't know who you were looking for, how would you find them ? Scroll through 10,000 records trying to remember their name ?

You stated It's no fun trying to PM or email someone spontaneously when the only sure-fire way to do it is to root around randomly and find a post by that person or hope that his/her name or handle is somehow referenced in the contents of a post to search for.

The same thing will happen with a member list, you will have to root around randomly through 400 pages looking for that someone.

Even as the admin, I have never found the need for a member list, I use the tools the board has, and they work well.