As long as it's just brushes you can use the "Scale Map" feature under "Tools" to scale it by a factor. If you use a normal factor like 1.5 or something it should even stay on the grid. It only scales what you have selected when you use it!
Emitters are problematic with this and Lights do get scaled but they scale both brightness and radius and somehow they end up not matching as they did before. Brushes work just fine though.
I think Doom's "lighting" was pre-painted on the textures. So you could do the same and use no lights at all.ok, tru to doom fashion, some areas are completely unlit, and some parts are lit by the small lightbulbs, but does this mean in the unlit areas, the walls will be bright, but the players will be black?