It would be good value- if it covered the full cost of the hotel [rather than just a discount].
The problem lies in dealing with London prices for the event (~50% higher than the rest of the UK), theres plenty other venues in the UK that'll provide an equally good event, with equally good transport connections- but without the London pricetag.
That being said, I'd probably get enjoyment from giving the money to a mod dev; I've had more fun hanging out with this pile of sweaty nerds than what I would in London.
The tickets on the door thing I can kinda understand, if that option was available you'd get a tonne of people turning up there on the off chance. Having a bunch of extra [disappointed] people around could make things somewhat more difficult to manage.