I agree with you here. There are very little public data that I’ve seen regarding legacy admissions and its influence on donation rates.
But let’s be real here. The universities obviously are calculating this. If there was no benefit from admitting legacy kids (ie no additional cash-flow), then they wouldn’t be doing it. Legacy admissions practices would be halted over-night. The fact that it has persisted for so long makes me wonder how big the ROI is on legacy. It must be pretty darn good. Especially at places like Harvard. They don’t need the money but their legacy admit rates are so high.