Your research is correct. If you are interested in Columbia or USC, go ahead and give it a shot this year.
However, a little experience would not hurt you -- especially if you're interested in Berkeley. If I were you, I would try to get some journalism experience this summer. It's not too late to find something to put on this year's application, to show you mean business. Call a local newspaper (daily, weekly, some type of publication that could use free help), tell them about yourself and say you'd like to write something. Volunteer to do some type of online news -- that's basically what I did last summer to have something recent on my app. (My clips were still nearing two years old, though.) Do something to get a clip or two, preferably three.
If you're feeling really confident, write some news stories on your own.
If you have taken any journalism-related classes in college, that would make your application seem less out of left-field. If you haven't, if you have time to take something this summer -- perhaps at a community college -- that would be a good idea.
Overall, don't overestimate the amount of experience you need. You only need enough to show you are serious about journalism, dedicated, and that you have potential. Passion can go a long way. I assumed my own "experience" wouldn't be enough (four journalism courses in a media / communications major, one year on a college newspaper staff as a writer and web editor, and one summer doing web news and communications work for a nonprofit), but it was!
Good luck!