I've been to the Whitby weekend a fair few times, and Im really excited about NMA playing next year. ;-)
It's true that there have been problems with overcrowding (mainly manifested in the queues for the toilets) in the distant past, but this is no longer an issue. If I've understood it correctly, the capacity of the whole venue is the same as the capacity of the main room. As its a festival type event, everyone won't be in the main room at the same time, not even for the headliners. So it's unlikely to be filled to the rafters (though Im sure it'll be nice and sweaty down the front... ;-)
Accommodation can be a problem, though - things tend to start to get booked up 6 months in advance (especially self-catering cottages - hotels/B&Bs might be slightly easier to get hold of.)