As I am sure others will note there is much more to it than even what you have mentioned.
For one thing as a rule and for sure a generality (based on my own personal experience) you are around more high performing people (to be clear not everyone but enough of them) to pull you up as well and be able to learn from them and be in a great environment (while at school and possibly after). (This applies to any 'top' school not just Harvard). Again very generally a top school is going to have overall a better faculty (or teaching assistants). Better facilities. More connections to hiring companies. (Well known, right?)
Later after you graduate a degree from a top University is branding and gets you exposure and better opportunities.
There is also the very positive branding and halo that one gets from going to a top school. It's part of the reason that even if Kia or Hyundai made a car that was as good as or better than a Porsche 911 it wouldn't matter.
In fact there is a saying I heard once something like 'Sophia Loren without a nose is not Sophia Loren'.
> Get rid of the selection process and admit less intelligent and less well connected people and those people won't achieve the same results.
As mentioned the branding alone is worth it's weight in gold.
That said important point is the value as with any branding is driven a great deal by the media and popular culture. (Super important point right off "IVY League" branding goes a long long way).