This whole 'tear down city hall plaza' thing is a lot like the new soccer stadium thread. There is no compelling reason to disrupt everything other than the aesthetics of the place. Day dream about what you want to build on that plaza all you want but at the end of the day a few trees, a play ground and a water feature might be the only thing that can actually go there without everyone having a massive fight and wasting millions.
If it's done right, it'll be an improvement and if people start using that space, it'll continue to improve. Over the years the actual city hall building has grown on me but the plaza never has. Some greenery will take the edge off.
Enough with the rounds of 'how do we improve this' and just actually try something.