Did they graduate in higher numbers? Did they have better career outcomes? Did more get into better(?) grad schools? What is their median income? Are they happier, did they enjoy college more?
As for what the improvements are like... hard to say. Some ways to improve the rankings like getting more students you don't want to come to apply (so you can appear more selective) don't actually help at all, while things like small classes even if done to "game" the rankings could actually help.
There's also just the cyclical aspect of things: the quality of your experience is going to be significantly determined by the quality of the student body, so if you have a better applicant pool because of your better rankings you maybe have a bit of a virtuous cycle that's somewhat disconnected from whether the things you changed actually improved anything real on their own other than the ranking.
If a school only admits students who have at least two years at another college with high grades, their graduation numbers will skyrocket.
A highly selective college, like Harvard, could even refuse to grant credit for those two years.
There are less nefarious ways of selecting a class of likely graduators: leadership in extracurriculars is highly correlated with post-secondary graduation.
Foreign students with limited English fluency have very low graduation rates. They could (should?) be excluded.
Those are officer training schools, so it makes sense they're ostensibly selecting for leadership skills, because they'll be overseeing enlisted recruits.
And make sure you control for your inputs. It's harder for the #2 campus of state school to wring "good outcomes" from the children of plumbers and truck drivers than it is for big brand name schools that have plenty of kids of doctors and lawyers in there to drag their average up because even if you do a middling job educating them and have squat for industry connections they will still land internships and go on to get good jobs.
In my opinion as a student who entered Northeastern in the mid 2010's the answer to all your questions is an unequivocal yes. More competitive student body, better profile to attract employers, more student amenities to enhance on campus life (we could have more in this regard imho). Compared to the commuter school of yesteryear it's for sure a much better educational experience.
Northwestern was already relatively prestigious.