I guess you could put UCSD in tier 1.5 or thereabouts; I don't think it has the same national recognition as UCB or UCLA, not sure about the academics as I haven't seen UCSD myself. As for UCSD being a party school, I don't recall ever hearing that, but I'm sure almost every school has been called bad things at one point or another.
The three tiers are pretty much what most people who follow college admissions think. I personally clump UCSB/UCD/UCI together in terms of ranking. From what I've seen at my school, outgoing social people who are smart want to attend UCSB.