If it wiped away defences it'd be more than worth it and Ukraine is now more than capable with its Shadow Storm missiles which UK provided just for this kind of attack.
It's a very bold move and if intentional it could be pivotal in this conflict.
It is an act of mass destruction and a war crime, that Ukraine was very worried about for some time since it will kill many innocent people. Very, very unlikely they did it. My first bet would be the dam failed from russian negligence / mismanagement, second the russians blew it up. But there will certainly be video of what happened today soon.
Cruise missiles don't win wars like this. It requires land forces crossing and holding territory. The narrower parts of Dnipro was the easiest path to doing that in the south.
Those cruise missiles were specifically designed to destroy tough targets like this dam.
If either side knew this was going to happen (because they planned it) it would certainly easily be the difference between winning and losing this war.
No. Storm Shadow has a small penetrating warhead. It is designed to punch through reinforced concrete to destroy whatever is within. It is not designed to destroy solid concrete. Otherwise the Crimean bridge would already had been destroyed with one of those super duper warheads.
It doesn't matter if the defenses are wiped out, if you cannot cross to reach those defenses. The terrain and roads will be wrecked and everything will be a muddy mess for miles.
It's a very bold move and if intentional it could be pivotal in this conflict.