I would expect the spikes themselves to wear down in a typical season of training and racing on all weather.
I would expect the spike plate to lose significant rigidity in about the same amount of time, so there is kind of no point in removable spikes in shoes like these.
Slightly heavier/cheaper spikes/shoes tend to last longer (thicker spike plate doesn't lose rigidity as quickly), so they may get through two or three sets of removable spikes before they're trash.
So for half the cost, you can have a set of shows that is 10% heavier but lasts 3x as long. As a guess, your time may be .5% slower or so, so figure about .05 seconds over a 100 meter race for an elite male 100m specialist.
For the typical high school athlete, it probably doesn't make sense to shell out for these spikes. But it sounds like she already has them, so she might as well enjoy having them and use them.