Hi Keith. There is no hard rule for when you should use displacement or when you can get away with just using bump/normal mapping. If your wall is made of large stones, you may want to use geometric displacement or else the stones won't look real at the wall perimeter. But if you sculpted details on the wall (paint blobs, picture frames, cracks, electrical outlets, etc) then you're probably OK to use normal/bump mapping as it will look nearly identical to the displaced surface but will render A LOT faster. The only time it would be a problem is if you rendered the wall from a glancing angle. Those details will then appear to be increasingly flat (as they are in fact painted on the wall). In situation like that, you need to use geometric displacement...

jonah

PS - 3DCoat now has an option to import the model without smoothing it. It was added for people working with CAD models...