I personally feel that you have to evaluate each one of these on their own merits.
The Little Free Library comparison is a good one, because they often sit in similar grey areas to Stobie Pole artworks. In my opinion, factors such as there being a clear delineation/boundary between the potential Wayspot and single family private residential property (like a fence, sidewalk, or council maintained landscaping) should be considered, as well as whether people interacting with the potential Wayspot would possibly interfere with the private enjoyment of nearby single family private residential property.
I think we also should recognise that from a game perspective, there is a strong incentive to accept these (rightly or wrongly) because it can transform unremarkable residential suburbs into Wayspot dense locations similar to inner cities other more dense locations. Stobie Pole artworks in residential areas are often readily accepted under the current status quo. You might find that you’re fighting an uphill battle against a lot of other South Australian reviewers should you take a hard “no” line with Stobie Pole artworks.
Unfortunately, I don’t think it’s possible to have a perfectly binary answer on how to handle these because each one is different.