I found that I can create levels much faster if I just keep everything as tiles, even the object spawn points. Instead of navigating in 3D, pointing to a place and clicking "Add Model", it's much faster to just use the 2D editor to place special voxel values and then have a Lua script spawn the models into existence. For episode 2, I'm creating the levels in the 2D editor, and last night I was able to make 2 levels in a matter of minutes. Before, in 3D, it took hours for each level. These new levels are much flatter and simpler, but they are also more expansive, with room to roam and freedom to strafe around the monsters.
I feel like sacrificing map detail for larger maps and increased design speed is worth it. I'd like to find out if that's true. It definitely makes the whole level design process feel much smoother. Adding the detail back in though, will be a challenge. Maybe higher-detail voxel chunks can be added sparsely in certain areas for things like staircases, buildings with windows and such.