Is taking summer college credit in prestigious colleges worth it for college applications?
No. These programs are pretty much cash cows for those institutions. Shelling out for a summer class won’t automatically improve your chance of admissions. And if you do complete the class and earn the credits, you will have to keep track of that one summer class’ transcript for the rest of your life.
Now, if there is a class that truly intrigues you and that you feel will allow you to stretch yourself intellectually and/or that will allow you to skip an intro. level class when you do go to college, it may be worth it for you to take that class. But then the institution won’t matter much provided it is accredited and the course is eligible for transfer credit pretty much wherever you’d be likely to end up.
Also, this summer everything will be online and you will be taking that class from your own bedroom/livingroom/back patio/etc. So the fun aspects of going to college for the summer - living on campus, hanging out with other summer students, etc. just won’t factor into things.