Berkeley and UCLA definitely put a lot of emphasis on visits. If you're in the US and anywhere near California, then you'd better visit and talk about it in your essays (Haas even has a short essay for you to talk about "how you got to know the school better").
With that said, most international students I've met so far have never visited Berkeley, even during admit weekend. So if you're international, you're fine. I do know a small percentage (probably 20% or so) of US students who never visited either, but they knew that Berkeley was their top choice when they applied, so they probably wrote a very convincing essay to that effect.
Even if you cannot visit, contact students from club websites. Talk to them on the phone, meet the local alums, do everything you can to learn about the school and incorporate it in your essays. That should do you just fine.