Your tune would change as soon as someone set up camp in one of the empty spaces.What you might call seedy, I call safer.
Placing a solid barricade down the middle of Harbor, disguised by Bushes... Parts of it are already there to prevent people from crossing the street. Adding K-Rail berms (4 feet high or so) next to the Sidewalk, not so much yet, But the new Magic Way Bridge will have that in parts. Las Vegas has done that at corners with very positive effects.
Since we are retrofitting, you need to have ramps to move people up to the bridge level, but still allow access to shops at street level.
The Las Vegas version have been given design awards and met with success on many levels
Getting physical barriers close enough to intersections to prevent people from using them means encroaching on visibility triangles, so not exactly safe.
While Venturi and Brown encouraged us to learn from Las Vegas, it has never been considered a very good urban environment. The first award you list is even for highway design, not urban design.