I respectfully disagree that it's a good expenditure of funds, or good value for marketing.
They need to generate positive hype for the game; hosting their event in a castle won't achieve that, not when they were determined already to put on a flashy panel show of some sort, which would be distributed and consumed digitally regardless of its actual venue, and not when many, many folks are already question whether Larian has bitten off more than they can chew, are in over their head, and are committing repeated mistakes of personal hubris along the way at every turn. A flashy publicity stunt for a game patch that is long overdue, and the end of a long string of broken words and statements and other misleading marketing, does not make them look professional or like they are doing anything other than flailing about hopefully.
Edit: Let me put it another way... The people who are already on board and hyped for the game are not the ones they need to reach or sell to. The patch itself will do that, as illustrated by the first half dozen comments in this thread. The people who are not interested and who haven't yet bought in on the game are not going to be won over by anything other than the actual content of the patch itself. The people who want to love the game, and who need to be given an infusion of hope and hype after the drought and disappointment are the ones that they need their update campaigning to appeal to the most - I'm in that group, and this drives me away, rather than draws me in.
