I'd be more than willing to be a part of a terrain day. It would need to have a clear goal though and a build up. I think if its a vague 'we're gonna build stuff and/or make stuff look like nicer stuff.' thats when you lose people's enthusiasm to be a part of it. Making a few odd pieces or anything that isn't unified like that will mean terrain days without something as impressive or immediately evident to show off.

There's a really cool ice themed realm of battle board. maybe a day of making ice themed terrain, or painting some of DL's grey terrain to fit an ice theme. There's also a lot of the red rock pieces. Maybe another day to do a wasteland/mars/manufactorum theme. By the end of anyone of those days, there will be a really cool themed table that can go up here or on the dlair site, and obviously will be used in the store, which will motivate people to show up for future terrain days. It would be cool if it got to the point where there was an ice table, and a mars table, a ruins table, a grasslands table, etc.