Re: The ferry should have blown up
I agree with the OP - never thought of it that way.
It would've given Talia/Bane some credibility with their plan. And -
Since Gotham was shown to be a 'Dog Eat Dog' type population with the ferry scene if they had blown up - Batman's reclusive 8 year absence would've had more depth too - had the ferries blown up he could've gotten terribly disenchanted with defending citizens who would blow eachother up if worse came to worse.