We learnt a lot at our 20-strong conference (well, I did, as I was the one who organised it and discovered the hard way what worked)
Mix people up and don't have large groups who all know each other sitting together all the time.
Have an ice-breaker to begin things. At one of our Christmas do's we had to find the answers to a list of questions, which involved milling around speaking to a lot of others and finding things out about them.
Have active participation in some things, sitting listening to presentations on others, space for blethering built in between fixed things.
Keep it moving!
I don't want to be a wet-blanket, but it is one thing to advocate several regional get-togethers, but who is invisaged as planning and organising them all? It is like drawing teeth to get volunteers, and GNHQ have plenty to do already. Adding one holiday (probably done by a travel agent!) is one thing, setting up one country-wide meetup would be a vast amount of work, let along half-a-dozen or so.