I suppose you have already seen this video,
http://www.youtube.com/watch?v=fjN2iEzlk6M
it is very similar to your set, with pulldownit you have to prefracture before computing, but this is not really an issue, the point is by using pdi you are going to get a fast, realistic computation of fracture, as you can see in the video if you need more resolution of fragments in some region, just refine it.
Create new geometry is a high cost process no matter if you do it before computing or during simulation, and probably you prefer to have the heavy process done before computing to get a much faster computation and be able to tweak dynamics parameters in an interactive way to adjust your final animation, dont you?