I'm not an authority on this, but here is what I know:
There are two clubs at UCI that play smash: "Fighting Gamers @ UCI" , and "Super Smash Brothers Club at UCI". These are the facebook group names, so you can look them up there.
Fighting Gamers @ UCI meets every Tuesday night like clockwork in the student center (the room changes so check the facebook page). The club is mostly MvC and SSF, but all fighting games are welcome. Myself and a few friends are there just for Melee and show up around 7:30 or 8. We bring 2 setups and usually have 3-6 people.
Super Smash Brothers Club at UCI also meets Tuesday nights. Sometimes they book a room at the student center. Sometimes it's at someone's house. Sometimes they think they booked a room but find out they didn't and get kicked out >.< From what I've seen they bring 4-5 setups and usually have 12-15 people. One of the setups is PM and the rest are Melee.
On Tuesdays when both groups are at UCI the smash players combine. Last Tuesday (4/29) we had 6 or 7 setups and over 25 people. I'd estimate about half were UCI students. The skill range is very broad: the worst have little/no tournament experience, the best players have been playing competitively since the beginning. Last time I recognized a couple of guys from the SoCal top 20. In other words, everyone is welcome.