How do summer programs influence my admission chances?

I am a Junior. I am first in my class, carry a 4.0 GPA UW, and have a 34 composite for my ACT. I do a solid amount of extracurriculars, but I haven’t cured cancer or done anything extraordinary. I am white and will not be seeking any financial aid (God bless my parents). Last summer, I was enrolled at Boston University and took Calc I. This summer, I am enrolled at Stanford and taking Multivariate Calculus and probably a computer science class. I plan to major in econ.

Assuming that I receive A’s in my two classes at Stanford this summer, how will my admission chances to Stanford be helped? Do they consider things like this as early interest in the University, or do they not really acknowledge it? Would getting involved with the school (working at a library, joining clubs, etc.) help my chances, especially if I apply EA to Stanford?