Even if public spaces go under utilized I'd argue that they still provide a great benefit to the community even if just psychological. In cases of under-utilization though just plain green space could do the same at a much lesser cost.
Centennial Square tends to be fairly empty unless there is an event going on but it's also A) not in a great location and B) has no shopping or really anything worthwhile bordering it. It's also completely open to the busiest street downtown. I'm surprised I'm saying it but the Uptown Square is quite the opposite and provides a nice place to relax, or eat for shoppers or people on a lunch break. People need a reason to use a public space and rarely do people travel out of their way to do so.