Ok, so this isn't an attraction the way people from the UK would expect. You can't take the family there for a rip roaring day out or anything, but it is definitely a spectacle which is well worth a visit, and we loved it.
I really enjoyed just pulling over on the road to see thousands of gnomes of all shapes and sizes, and the messages people have left with them. Its not a commercial attraction at all, you just pull over and look around, and leave a gnome if you have one.
On the way back to Bunbury, we stopped at a brewery called The Moody Cow for lunch in their restaurant which was superb, but there are any number of wineries and breweries in this area where you can stop and make a bit more of a day of it.
Go on, go to Gnomesville, and don't forget to take your own Gnome to leave there (and a marker pen!)