One way in which fisheye lenses can be used is by capitalizing on their extreme depth of field to take a relatively small detail and make it large relative to the background. In that sense, it lets you emphasize details more strongly than you might with a rectalinear lens. For example, this is not a particularly interesting photo bit it may give you an idea of my point.
This allows you to emphasize a particular portion of an image, while shrinking away the rest into a background, much as those characatures of maps do, that emphasize (say) NYC as 80% of a map with the rest of the world just a tiny portion.
You say you do not shoot people, but it's angle of view means with just a bit of height (here just on a monopod held slightly over my head) you can get a view of people that is fairly unique, and de-emphasies individuals just by putting them in such a large context.
I bought the fisheye mostly for a few fun shots, but I do find it surprisingly useful, especially for variations such as the last (a reverse case is lying down and having an athletic team huddle above you - you can get the entire team's faces in looking down - but that's people again). I think for street photography it can be useful, but you are going to have to find the creative angles that capitalize on it, as opposed to having it just distort things and be confusing.