Hi Fred, Unless you want to put down some insulation on the floor I wouldn't worry about a plywood subfloor. You may have to take care of any moisture with a spray water proofer and some 6 mil plastic if you have a moisture problem. You probably know how to do the moisture test with a square piece of plastic or foil taped on all 4 sides down to the floor (and walls) and pick it back up a day or two later to see if moisture condensed under the plastic. Moisture under the plastic comes from the floor/wall and moisture on top comes from the house.
That said, most basement floors aren't level and usually slope towards the drain a little. This means you may be laying down some 1by2s with shims, etc. to find a level surface but some floor levelor makes the most sense. You may get lucky cause your mansion was probably quality built with a level floor or level enough you wouldn't notice a difference. I personally wouldn't be afraid of a laminate like pergo knowing that it would have to be replaced after the next hurricane floods the basement.