>> I'm sure if the said parent had not donated the 2.5 million dollars, not a single thing would have been different for the students. Not one.

That's definitely false. Most universities tie annual endowment spending to total endowment size. Just because you can't directly tie the dollars to a specific project, doesn't mean it didn't contribute to the general student body's quality of education.

What are you talking about, of course sourcing new endowments allows them to build more things/provide more services/etc. Approximately half of Yale's operating budget comes from revenue generated by its hospital system (which is a whole 'nother contentious issue, but besides the point). The other half largely comes from drawing a "safe amount" on it's endowment principal, i.e., small enough to be sustainable in the long term without depleting the fund. A relatively small part comes from tuition. Obviously, increasing the endowment (be it $2.5MM or $250MM at a time) increases the amount that can be put towards budgeting in the future -- enabling, for example, the University to grow its student body (which Yale is currently doing) while maintaining the ability to privately subsidize student tuition.