I think the level of media coverage is entirely predictable, and given the nature of the attack and the subsequent manhunt and shootouts, not all remarkable.
I do agree with you that in principle offering such coverage is a victory for the terrorists - this is exactly why they strike at such targets, to gain maximum media exposure, to create the greatest climate of fear, but given our 24/7 news coverage this is a genie our of the bottle - it cannot be stopped.
When it comes to 24/7 coverage, what i object to most is the febrile speculation that surrounds such events - again, inevitable i suppose - which distracts and misinforms - and the interminable parade of "experts" in one field or another related to explosives, or policing who ,even with their expert knowledge can offer little to really inform the debate at such early stages.
But the whooping and hollering was spontaneous, and i think was pretty understandable - terror and fear, a rolling, breaking news story with additional shoot-outs, the prospect of more killings, and the imposition of a curfew in Boston - unheard of in modern day US.