Luthor blew up the hearing to make it look like carnage follows Superman where ever he goes (even when he's being law abiding and diplomatic) it killed an outspoken ex-Wayne Enterprises employee whom Bruce was sympathetic toward, plus it killed Holly Hunter who had stated she was going to fight his acquisition of "a weapon of assassination" and it covered his tracks of said acquisition by also taking out the one Senator who gave him full access to everything.
Your first point would make some sense, but none of the really straight-forward, exposition-providing news coverage mentioned that that I could see. So, I don't think that was the intention.
Regarding the Wayne employee, it was obvious Superman had nothing to do with it, and Wayne would know that. And did Lex know Wayne was Batman even at that point? Did Lex know Wayne was Batman at all? It's all so confusing.
Regarding Hunter, Luthor already had a plan to unilaterally attempt to kill Supes, and was going to do it no matter what. I can get why he sought Congressional support in the first place--if he were rational, then he could place the blame elsewhere. So it was petty revenge, and that was obvious with his jar of piss. But that doesn't explain the complex, long-developing plan of orchestrating this explosion.
As Fabio says, it is somewhat effective as a tense, shocking moment in the film. But for what storytelling purpose? Joker always had a pretty obvious reason for the things he was doing, even though he was obviously nuts and just wanted to promote anarchy.
Not sure what you mean by "circular preaching to the choir stuff" exactly, but that was my thoughts going through this movie--people just weren't acting like people act. Not even movie people.
