I disagree to a point that the "like" phenomena is ValleySpeak. It may have evolved from that, maybe having it's roots there, but it is different. I was born and raised in the San Fernando Valley, which is where ValSpeak originated. The Frank Zappa song "Valley Girl" mentions a lot of places that I hung out at. I remember hearing it all over, long before the song and some movies made it a phenomena.
To me the "like" seems to be more akin to someone saying "uh" when they speak. It's a pause word while they think ahead on what they're saying. Something to fill the dead air. Well, that's not completely true, but I've noticed that if you were to take the full sentence that they said, and just deleted all of the "like"s, they are mostly complete thoughts and grammatically correct. Not always, but many times it is.
ValSpeak on the other hand seems to me to be a complete bastardization of the language. It is it's own dialect.
While listening to the "like girls", I had the thought that if my ears had a "like" filter that I could switch on, their conversation would actually be an intelligent and cogent discussion of school, their classes and teachers, and events in their friend's lives. But WITH the "like"s, they sounded like complete idiots.
Also, the bell idea is a great one and does work. I used to be in Toastmasters to learn how to better speak in front of people. One of the tools used is that someone will literally sit there listening to your speech with a bell in hand. Any time you say "uh", or "um", or any other placeholder noise or word, they ring the bell. The number of ringings is tallied and counts against your score for the speech. It's an extremely effective tool and teaches you very quickly that a small pause makes you sound much more intelligent than continually tossing in "uh", "um", "duh", or other noises.