Big fan of SSP, both my kids attended. SSP is real research, but as you note, it is not original cutting edge research that is going to result in publication, unless you were to substantially expand beyond the base SSP project after the summer on your own time.
SSP students do have a high admission rate to HYPSM and others, but that’s as much a testament to the strength of the students admitted to SSP as it is an effect of attending the program. While elite college admissions folks are going to know what SSP is, it is not a magic bullet to admission – particularly now with recent expansions of the program to serve over 400 students each summer.
You should choose the research program that you are most excited about spending large amounts of your time on this summer, and not on how you think it might appear on your college application. Good luck!