Regarding the smoke, another issue is the shape of the building itself. With the aircon system, and knowing that heat and thus air rises, any large amount of mist or vaopur has the likelyhood of travelling upwards - and fogging the roman scenes.
Those who recall the Cronkite (and Perrin) versions will remember the ascent vortex used to be filled with fog, so think you couldn`t see cars in front of you. It was designed to clear just as the overhead burst animation of lightning appears. The issues with airflow taking the smoke either into the dawn of time, caveman (or even the egyptian) scenes was a major factor in rethinking the effect in 1993/4. Not to mention the times load would become misty if the smoke blew downwards on a blast of cold air.
The short lived 180top laser effect in 1994 was also deactivated since this used water vaopur to create mist; it began to corrode metalwork. Same as E:E. Not to mention it would cause escape stairs to become slippy (also found in WDSPs RnRC). Mist effects have to be carefully thought out. As an aside, Revenge of the Mummy at USF uses 13 different types of fogging effect depeding on the effect needed and its placement. You can`t just turn on a smoke machine.