Bandaid-ing plants and naively making public spaces often doesn't work in the US. It's a little more work to make spaces where people actually want to be.
Look at the numerous existing city public spaces built into high profile architecture, where basically no one ever hangs out in. (There's a TED talk about this.)
Why would their worth be determined on how many people hang out there? I prefer to see green spaces and am okay appreciating them from a distance, such a in a nearby town with a tree lined main street through town. I don't think it would invoke the same aestetic pleasure with people and litter occupying these spaces.