Hrm, I think you might be ignoring the cost of actually doing the calculations, unless I'm missing something. The value of simplifying assumptions comes from how much easier it makes a situation to model. I guess the question would be, is the effort saved in modeling this thing with an approximation rather than exact figures worth the risks of modeling this thing with an approximation rather than exact figures? Especially if you have to do many models like this, or model a lot of other factors as well. Such as trying to sort out what are the best ways to spend your time overall, including possibly meteorite preparations.