No, I only used the 9-18 behind the Zen dome. Never really even crossed my mind to put the diopters on the 9-18, but then again, I'd need a different set. The 9-18 does not have 37mm threads, I forget the exact size.
The 9-18 is fairly wide and focuses relatively close, so can't imagine too many cases when I can't get close enough with it. You would have to be taking a picture of a completely static subject before focus distance became an issue.
Phil, I would say you have summarized my feelings on it.
If I don't get a dedicated macro lens, I'll keep in my bag as an option.
It can be handy for getting shots of skittish creatures where you need to stand off anyway.
I actually got a fairly nice blenny pic, but stupidly deleted it from the camera before I downloaded.
Moral of the story: don't drink wine and review pics on the camera before downloading.