Whether these extracurriculars would expose you to different ethnicities and world views is dependant on demographics.
I have never heard of community service as a requirement to graduate high school. (No school in my district had this requirement.)
Granted, I understand your overall point. It is becoming increasingly difficult to be accepted by "elite" colleges. In fact, I had applied to nearly 12 colleges that were highly respected in Computer Science and was rejected from all of them.
http://patch.com/california/redlands/2016-top-100-public-hig...
None of the top ten schools on that list seem to have a community service requirement [0].
There doesn't seem to be a hard and fast rule regarding which schools do or don't have a community service requirement. Mission San Jose does, but Lynbrook does not.
[0] As determined by a quick google search for each to locate "$SCHOOL_NAME graduation requirements", followed by a quick scan for anything outside of required course credits.
Either way, your statement about the top 10 CA high schools is false. I attended Granada Hills Charter and San Marino high school (#1 and #7 respectively) and both do absolutely require community service. San Marino requires 40 hours over four years [1] and GHCHS requires 20 hours per semester [2]. A friend at Miramonte High School didn't have to do any community service but I recognize many of the schools on this list and can confirm they require community service. Searching for "graduation requirements" just gives you a list of credits you need but doesn't include community service or disciplinary rules for graduation.
[1] http://www.sanmarinohs.org/apps/pages/index.jsp?uREC_ID=2241...
[2] http://www.ghchs.com/UserFiles/Servers/Server_20226865/File/...
But sure, it looks like my naive search approach is inadequate, as it for the most part brought up credits (as you mentioned).
And to be fair, I don't think charter schools should be lumped in with the rest of the public schools, but that's probably just my opinion.
[0] http://cc.sduhsd.net/Counseling/Community-Service/ [1] http://www.lhs.fuhsd.org/resume
It's a general state-wide requirement in Maryland, for example. See http://coursebulletin.montgomeryschoolsmd.org/Home/Introduct... for reference.
And that's been the case for at least 20 years now.