Valley-girl speech *Redux*

[nq:1]There has been much discussion in Usenet of the peculiarity of speech shown by some younger people wherein they have a rising intonation at the end of a declarative statement, making it sound like a question.[/nq]
Bob Cunningham's thread lasted about four days, running May 12-16 and got sidetracked with cross-posting.
So I'm a johnny-come-lately, but I have something to say about this subject, interest petered out with Bob's thread, so I'm just starting this new thread.
I'll give you all a U.S.A. California perspective circa 1970-1971. It's not originally a Valley-girl thing.
After I returned from Vietnam in 1970 and set up housekeeping on Treasure Island (then and now part of San Francisco), some teenagers lived with us. They picked up that rising intonation from the local teens, and I tracked it down to the influence of the dope smoking, maggot infested, hippy culture in the San Francisco Bay Area at the time. I lived in and visited San Francisco at various times 1963-1971 and I witnessed the cultural, social and linguistic changes, and I am absolutely certain of this.

I've concluded that the rising intonation comes from the politically correct desire to be seen as non-judgemental which is supposed to be cool and it means, "you know man..., you know what I mean man..., whatever you say man..., let it all hang out..., go with the flow", and all that crap. The rising intonation injects a little bit of doubt, a little bit of tentativeness, a little bit of the interrogative into the declarative statement. I tried to break the kids of the habit, but was not entirely successful and now one is an adult of 50 and she still speaks that way.

Dennis Hopper in the role of the hippy journalist in "Apocalypse Now" spoke that way, so you can get an idea how far back this self-inflicted speech impediment goes.
The generation of the 1970s passed it on, so that many American kids of 1980s and 1990s have acquired this annoying habit of speech. I always thought it sounded whiny.
Valley-girl speech has incorporated that annoying habit of speech, but to me the rising intonation is not the sole distinctive feature of Valley-girl speech.
Another misuse of the English language occurred at about the same time, that is the incorrect use of "may I" and "can I". It goes like this; student in line at school cafeteria asks; "Mmmh, uhhh, can I have a tuna sandwich?" If I was the cafeteria line server I would reply with "Yeah, sure" and then go on to ignore the student. I hear this daily all over the U.S. If the student asked why he didn't get a sandwich, when he asked "Can I have a sandwich?", I'd say; "Sure you can. Anything is possible."
Just think, some of the American kids of the 1970s and 1980s that adopted that whiny, rising intonation in the declarative statement went on to become public school teachers, doctors, lawyers, movie stars and congress-creatures.