if you got rejected from LA “engineering” but got accepted to UCD / SB, I think people would understand you appealing…but SD? it’s like got into MIT (UCSD much much bigger engineering school) but rejected from Caltech (much much smaller engineering school). Why would you want to appeal just for the environment and undeclared major? As far as program goes UCSD’s comp sci is at least on par if not better than UCLA’s. As a matter fact, I think engineering/science school and students quality in California would rank like this Caltech / HarveyMudd / Cal > UCSD > UCLA > USC. I think the students who actually got into their engineering schools at least from academic point of view, they are better than UCLA’s engineering/science kids. Just look at their average SAT math for the last year. and that’s just average SAT math that’s already higher than UCLA’s. then picture the average SAT math score for the folks who got into their engineering school (impacted majors). http://admission.universityofcalifornia.edu/counselors/freshman/profiles/index.html
And also look at how many Nobel laureates in their short history comparing to UCLA’s.
I think you are very fortunate to get into their CS department, truth to be told.